Wednesday, August 22, 2012

Returning Humidity & Watching Isaac

By Jay Grymes & Steve Caparotta

Just like yesterday, most of us stayed dry, but several of the coastal parishes dealt with showers and t-storms as a weak, quasi-stationary front continues to hug the coast.  In fact, the NWS posted a Tornado Warning for areas near Grand Isle during the afternoon as a severe storm showed indications of rotation! While there were no confirmed reports of a waterspout or tornado, a 53 mph wind gust was measured on Grand Isle.

With the front lingering along the coast into Thursday,  we could see a couple of showers continue there well into the evening.  But for most of us, it should be a fairly nice evening and a mild night ahead.
Many along and north of the I-10/12 will wake-up to the upper 60°s on Thursday as we enjoy one more day of slightly-lower humidity before more typical August weather returns.  But the coastal front will dissipate during the day, winds will swing around to the southeast bringing in Gulf moisture and we’ll say goodbye to the run of slightly drier air.  But the air won’t “moisten” all that rapidly, so we’re calling for only isolated afternoon showers on Thursday under otherwise partly cloudy skies, with highs in the low 90°s.
Set rain chances at 40% for Friday, then back them down to 30% for Saturday and only 20% for Sunday.  Sunrise temps will be near 70° to the low 70°s with highs in the low 90°s for all three days.   Our forecast remains mostly-dry for the first part of next week as well.
Meanwhile, more and more attention turns to the tropics. 
Tropical Storm Isaac is rolling through the Lesser Antilles this afternoon and is headed into the warm Caribbean.   While Isaac is a fairly large system, it is not especially well-developed as yet.  The model forecast consensus and the NHC 5-day projection still keeps Isaac heading towards Florida, although there should be some significant interaction with the Greater Antilles (mainly Hispaniola & Cuba) to slow any intensification.  

A threat to the eastern Gulf certainly can’t be ruled out and we are far from ready to sound the “All Clear” for Louisiana.  But for us, it is too early to get too concerned up about Isaac.  Still, be aware that there is a fairly good chance that Isaac gets into the SE Gulf by Monday.
And east of Isaac, the NHC upgraded the next tropical system to T.D. #10 earlier today.  Thankfully, early indications are that T.D. #10 does not appear to be a Gulf threat.  However, the 5-day outlook for #10 does suggest that the U.S. East Coast needs to remain vigilant with that system as well as Isaac!

Monday, August 20, 2012

Tropics getting very active!

How about the “drier,” less humid air? Well, we certainly deserve it, especially after some of the rains that many of you endured over the weekend!

Our current drop in humidity made it almost comfortable outside this afternoon ... we said, “almost!” And with dew points expected to stay in the 60°s for the next couple of days, we’ll get to enjoy some pretty nice mornings and tolerable afternoons -- by August standards -- into mid-week, at least.

The ‘cool’ front that we’ve been watching slowly -- and we do mean SLOWLY -- sag southward over the past four to five days looks like it will ease its way out into the coastal waters later tonight and into Tuesday morning. “Drier” continental air will remain in place over most or all of south Louisiana, delivering a much-appreciated break from our typical August heat-and-humidity.

So then the question becomes: how long before the humidity returns?

It looks like the front will stall tomorrow along or just south of the Louisiana coast, then begin a slow landward retreat on Wednesday. That should allow for at least two fairly decent days for most of the WAFB viewing area, with more typical Gulf humidity likely back in play for just about everyone by Thursday. Along with the humidity, we can expect a return for typical summer-season rain chances as well by week’s end.

Our locally quiet and favorable weather is quite the contrast to all the action happening in the tropics! We now have four areas of interest, including one in the western Gulf.

GORDON has been a bit of a surprise during his lifespan, reaching Category 2 intensity and hanging on to hurricane strength for 48 hours or more. Downgraded to a tropical storm this morning, GORDON continues marching east across the Atlantic, having made “landfall” and passed through the Azores earlier today. Forecast thinking for GORDON is that shearing winds and cooler waters will lead to ‘his’ fairly rapid demise, and GORDON could be declared as “post-tropical” as early as this evening or tonight and will likely dissipate in the next few days.

An area in the western Gulf of Mexico has been dubbed “Invest 95L” by the National Hurricane Center (NHC), and an Air Force Reserve Hurricane Hunter is currently in the area and taking a closer look. While 95L appears to have some association with remnants from the weekend’s landfalling T.S. HELENE, the NHC designation indicates that it will be considered as a new and unique system should it become better organized.

95L has been showing some hints of a broad mid-level "spin" but it doesn’t look like that the spin extends to the surface. It's also dealing with wind shear, may be pulling-in some dry air, and appears linked to a non-tropical trough extending to the northeast across the Gulf. Whatever it is, 95L does not have the classic look of a healthy tropical system, at least not yet. And as of 4PM, we haven’t seen anything from the Hurricane Hunter that would suggest a “closed low” or an upgrade to TD #10. (If this system does become upgraded, it will get a new number and ultimately a new name and not be defined as a “comeback” by HELENE.)

There are two “Invests” in the tropical Atlantic: 94L and 96L. 94L is roughly 1000 miles east of the Lesser Antilles and is tracking essentially due west, likely reaching the Lesser Antilles in the next two days or so. A long-range consensus forecast takes 94L into the Greater Antilles by Friday and into the weekend. Although that is quite a ways down the road, we’ll be keeping a close tab on 94L as there is some potential that this could become a storm of concern for Gulf interests.

96L is located southwest of the Cape Verde Islands and also appears to be on a westward course, riding along the ‘Tropical Easterlies’ behind 94L. But given its location, there is no need to be concerned about 96L for now.

Yes ... we are in the second half of August, the time of the Hurricane Season when action can really pick up. Are you ready should Louisiana come under a tropical threat? There is still time to get prepared!

Friday, August 17, 2012

Wet Pattern Extends into Next Week

By Jay Grymes & Steve Caparotta

Scattered showers and storms tracked across the WAFB viewing area during the afternoon, with the a few ‘strong’ storms embedded within a general WNW-to-ESE movement. Unlike the previous two days, when most of the rains occurred to the south of Baton Rouge, today’s rains and storms developed on both sides of the I-10/12 corridor. Fortunately, while the storms did play a little havoc with the evening commute and some of the storm clusters became rather strong, we did not see any storms achieve “Severe” thresholds (as of 4PM).

The afternoon and early evening rains should subside by/before sunset, but we’re keeping a very slight chance for some overnight showers in the forecast, with spotty to isolated showers in the sunrise forecast (mainly closer to the coast).

We’ve been calling for a “wet” weekend just about all week long, and we’re staying with that forecast. Set rain chances for Saturday and Sunday at about 60% to 70%. These won’t necessarily be all-day rains, but we are expecting the weather to be a little busier throughout both days compared to the mainly-dry mornings and scattered-rains of the past couple of days.

In fact, there will be a somewhat better chance for rain on Sunday morning compared to recent mornings: keep that in mind as you head out to church services, to that family breakfast, or if you’re going to try to sneak in a few holes on the golf course.

We’ve been talking about a cool front as a primary focus for the weekend rains, calling for the front to sag south of BR and possibly stall over the coastal waters by Monday. As of this afternoon, it looks like the front will struggle to get even that far south and may remain draped over Louisiana, not only through the weekend but also for the better part of the work week. If that occurs, not only do we NOT get any relief from the humidity, but we keep pretty good rain chances in the forecast throughout the upcoming week.

Yes, folks, it’s looking rather wet through the next 5 to 7 days.

In the tropics, we have three areas of interest. T.S. Gordon ran into a little shear earlier this morning and has thus far failed to strengthen into a hurricane as projected yesterday by the National Hurricane Center (NHC). At best, Gordon may have a small window to make ‘Category 1’ intensity before shearing winds and cooler waters start to take their toll, but the latest NHC forecast has taken hurricane intensity off the table. Gordon will maintain essentially an easterly track over the coming days, and that could mean tropical-storm force winds for the Azores Islands late Sunday or early Monday.

The remnants of T.D. #7, located in the western Bay of Campeche, organized enough today to be upgraded to Tropical Storm Helene. The Hurricane Hunters found a small center of circulation with maximum winds around 45 miles per hour. The official forecast calls for Helene to move inland into Mexico on Saturday, but there's an outside chance the storm could linger along the Mexican coastline into the weekend. Either way, Helene doesn't appear to be much of a threat to the northern Gulf Coast at this point.

Lastly, way, way out in the eastern Atlantic, to the south of the Cape Verde Islands, a healthy looking tropical wave has been designated as “94L.” Regardless of what transpires with 94L over the coming days, it is simply too far to our east to be concerned about, at least at this stage of the game!

Have a great weekend ... and as always, a big “THANK YOU!” to all of our Weather Watchers!

Thursday, August 16, 2012

Rainy Days Ahead...

By Jay Grymes & Steve Caparotta

As expected, today’s shower-and-storm activity was a little more widespread than what we saw on Wednesday, with a few of the storms over the southern parishes getting a tad on the ‘strong’ side during the mid and late afternoon.  But as we’ve seen each day, most or all of the rains should subside by sunset.
However, our forecast for the coming days remains wet -- we’re going with a 50-50 rain chance for Friday and even better rain chances for Saturday and Sunday.  All of this will be triggered by a southbound cool front that will slowly sag through the lower Mississippi Valley from Saturday into early Monday.

Based on what we see right now, it looks like the front will push south of the Baton Rouge area and make it as far south as the coastal waters by mid-day Monday.  But then it stalls and hugs the coast through the rest of the work week.
We’ll see a modest dip in the humidity after the front passes, but not a huge change.  In addition, with the front meandering along the coast through mid to late week, it will be close enough to keep our weather unsettled.  As a result, we’ll keep scattered rains in the forecast throughout the week.
T.D. #8 was upgraded to T.S. Gordon earlier today.  Gordon has already taken his turn to the northeast and east, which means ‘he’ will be no threat to land.  But the National Hurricane Center believes that Gordon will slowly strengthen over the next 24-36 hours or so and calls for Gordon to become a hurricane.

Gordon is the season’s 7th ‘named’ Atlantic storm.  As has been true since May, the 2012 Atlantic Hurricane Season remains well-ahead of the long-term average in terms of storm counts for mid-August.  Historically, the 7th ‘named’ storm doesn’t develop until mid-September, and if Gordon does become a hurricane, ‘he’ would be the third hurricane this season.  By comparison, the basin’s average date of the 3rd hurricane is not until September 9th!
We’re also watching an easterly wave over Central America, the remnants of T.D. #7.  Some of the wave’s energy has emerged over the southern Bay of Campeche today as it tracks to the WNW or northwest.  While development can’t be entirely ruled out, the wave’s relatively rapid movement coupled with its proximity to land should inhibit any significant intensification before it moves onto the eastern Mexico Coast.

Wednesday, August 15, 2012

Rain Chances on the Rise...

By Jay Grymes & Steve Caparotta

Much like we saw on Tuesday, afternoon showers and t-storms were limited in coverage.  Most of Wednesday’s showers and storms moved along west-to-east paths in response to the zonal flow at mid levels.  And also like Tuesday, the daytime heat-and-humidity was the main weather story for most WAFB neighborhoods.
Our forecast for Thursday reads much the same, with slightly better chances for a cooling rain shower or t-storm over your backyard: set Thursday afternoon’s rain chances at about 30% to 40%.
The current quasi-stationary front draped over Louisiana is expected to begin a slight northward retreat tonight and tomorrow and effectively dissipate to our north, keeping the WAFB viewing area under the influence of this very warm and very humid Gulf air mass through the remainder of the week.
By Friday, a deepening upper-level trough over the eastern U.S. will help drive a cool front south-southeast across the U.S. Plains -- that front will become the main weather feature for us as we head into Friday and the weekend.  We’re going with 50-50 rain chances for Friday afternoon.  That same front is expected to slowly work its way southward through the state, providing lift for the unstable air mass during Saturday, Sunday and Monday. 
With the slow-moving front over us, we’ll keep high rain chances - - 60% to 70% - - through the weekend forecast and carry a 50% to 60% chance through Monday!  By Monday afternoon, many WAFB communities could be dealing with multi-day rain totals on the order of 2” to 4” or more!

The latest guidance suggest that the weekend front will eventually pass to the south of Baton Rouge, possibly making it into the northernmost coastal waters early next week where it is likely to stall.  This should give us a brief break from the very-high humidity we’ve endured this week, with morning lows possibly dipping below 70° for communities along and north of the I-10/12 corridor.
But if that relief from the humidity does develop, it only lasts a day or so.  By mid-week, the humidity of the Gulf air mass will quickly return.
The disturbance over the central Atlantic -- roughly 600 miles ESE of Bermuda -- has really taken shape over the last 12-18 hours or so and has been upgraded to Tropical Depression #8 as of 4PM.  The NHC forecast calls for additional strengthening, with TD #8 potentially becoming T.S. Gordon later tonight or tomorrow.  Regardless of what does become of TD #8, virtually all of the computer guidance has it taking a hard turn to the east in the next day or two, which means it stays out over the open water with no threat to land.

The remnants of T.D. #7 still has our attention even though the core of the wave is over the Central American landmass.  There remains a slight bit of concern that some of the energy associated with this tropical wave could emerge into the Bay of Campeche in the next day or two.  Even if this did occur, it appears as though its current WNW track and forward speed -- at 15-20 mph -- would give it little time for significant development before moving back over land along the Mexico Coast.  Regardless, the system looks like it will continue to be a troublesome rainmaker for Belize, Guatemala and southern Mexico in the coming days.

Tuesday, August 14, 2012

More Heat, Isolated Rains Through Thursday

By Jay Grymes & Steve Caparotta

The heat and humidity made for another uncomfortably hot day on Tuesday, and only a few neighborhoods were lucky enough to get some mid-afternoon cooling showers to break the stifling air!  Tuesday’s Heat Index for Metro Airport was already at 95° by 9AM and climbed above 100°before 11AM!
We’ve seen some locally-heavy rains in and around metro New Orleans today, prompting some NWS advisories, but only very limited action anywhere along and north of the I-10/12 corridor as of 4PM.
And we’re expecting a repeat of today’s weather pattern for both Wednesday and Thursday around metro Baton Rouge: morning minimums in the mid to upper 70°s, afternoon highs in the low to mid 90°s, Heat Index readings at or above 100° for upwards of 5-6 hours or more, and only a handful of communities getting an afternoon rain.  For now, we’re calling for no better than a 20% rain chance for the next two days.
A weak and dissipating quasi-stationary front will continue to linger over the Bayou State for the next two days.  Although our afternoon conditions will be hot-and-humid, this weak front will not provide any significant additional lift to get more widespread rains going.

All that changes towards week’s end, however, as another cool front will sag southward and into Louisiana.  Our early guidance suggests that the weekend frontal boundary will have at least some chance of pushing through most or all of Louisiana before dissipating early next week.  But this slow-mover will take its time crossing the state, and that will mean improved rain chances from Friday, through the weekend, and even into Monday.
We’ll have to keep an eye on this developing weather set-up:  while it is far too soon to become concerned as yet, this scenario has some potential to be a fairly serious rainmaker over a 4-5 day period.
And in the tropics?  Remnants of T.D. #7 are moving inland over Honduras and Nicaragua this afternoon and evening, leaving no chance for re-development for this tropical wave.  Still, it is likely to be dump copious amounts of rain and produce flooding for portions of Central America.  And in the central Atlantic, roughly 850 miles southeast of Bermuda, a low-pressure area appears to be getting better organized.  The National Hurricane Center has “upped” its chances for tropical development in the next 48 hours to about 50-50 as it continues to move NW or WNW.  But all the early tropical guidance for this system has it getting caught in the Westerlies (West-to-East flow in the mid-latitudes) over the next couple of days, which means no threat to Bermuda or the U.S. East Coast.

Thursday, August 9, 2012

More Rain on Friday

By Jay Grymes & Steve Caparotta

The active afternoon weather should settle down later this evening, but plan on a return of showers and storms for Friday -- we’re setting rain chances at 50% for Friday afternoon.  A cool front is still expected to sag southward into the viewing area tomorrow, then stall and linger over the viewing area through most of Saturday.  Our thinking is that the stormiest period will be prior to the front’s arrival (Friday), and that the weather will be a bit quieter on Saturday.  Our Saturday forecast calls for a sun/cloud mix for much of the day with isolated mainly-afternoon t-showers.

 The front is expected to weaken and begin a retreat northward late Saturday into Sunday.  Although we won’t see any big changes in the afternoon temperatures, we should experience a modest dip in the humidity late Saturday and Sunday -- while highs will reach the low to mid 90°s on Sunday, the drop in humidity levels will be most welcome!

Rain chances will then begin a slow rebound starting Monday and extending into the middle of the work week.

T.S. Ernesto failed to return to hurricane strength, mainly because ‘he’ remained too close to the coast.  Ernesto made ‘his’ final landfall earlier this afternoon, and the 4PM Advisory from the NHC had maximum sustained winds down to 50 mph.  Ernesto will continue to track deeper into Mexico tonight and interaction with Mexico’s mountains should bring a quick end to the storm system.  However, locally heavy rains may continue, prompting flood worries there.

In the central tropical Atlantic, the area we’ve been watching for a few days has been upgraded to Tropical Depression #7 as of 4PM.  Although TD #7 remains a long, long way east of the Lesser Antilles, the current NHC forecast brings the system right into the eastern Caribbean over the weekend.  In addition, the forecast calls for TD #7 to become a tropical storm (T.S. Gordon) within the next 24 hours.

 And in case you haven’t heard, the NHC and NOAA tropical experts have “upped” their storm count forecast for the current tropical season.  In late May, the NOAA folks posted a forecast calling for 9-15 ‘named’ storms with 4-8 becoming hurricanes.  Earlier this morning, NOAA adjusted those numbers to 12-17 ‘named’ storms, with 5-8 becoming hurricanes.

Wednesday, August 8, 2012

August 'Cool' Front?

By Jay Grymes & Steve Caparotta

Titan9 Doppler has been tracking one of the more “textbook” seabreeze fronts we’ve seen over south Louisiana in quite some time.  The line started taking shape before lunchtime and continued tracking northward at about 15 mph through the early afternoon, arriving along the I-10/12 corridor a little after 2PM.  Although none of the storms in the northbound line reached ‘severe’ status, locally-heavy rains over several southeastern parishes prompted the NWS to post local Flood Advisories for a number of communities. 
As well-defined as the line was at 1PM, by 2PM it was weakening, and all but collapsed between 2-3PM ... before reaching the Baton Rouge area.  That will leave the WAFB viewing area with a few showers and isolated t-storms for the remainder of the afternoon and early evening, with most, if not all, of the rains dying out by or before sunset.
We’re raising rain chances a bit for Thursday -- to 40% -- and going with a 50-50 chance for rains on Friday.  It looks like a ‘cool front’ will try to dip all the way down into our viewing area from Friday into Saturday.

To be honest, Jay was a little skeptical that the front would get this far south, but after two days of runs suggesting that it could get at least as far south as the Florida Parishes, he’ll “bite” on that projection today.  But the front does not look to get much farther south than that, and it likely only gets that far for a handful of hours before becoming stationary and then beginning a northbound retreat.  As the front approaches, we expect to see a modest and welcomed dip in dew points (slight surge of drier air).
The outlook for Saturday will be dependent on the details and position of the front: we’re thinking that Saturday will be dry for most neighborhoods but with a sun/cloud mix through the day.  But the forecast for Sunday looks very promising!
Ernesto made landfall early this morning and was downgraded to a tropical storm by 4AM.  ‘He’ has spent the entire day over land during his westward trek across the Yucatan, and that has produced additional weakening.  As of about 3PM, the center of the system appeared to be emerging over the extreme southern Bay of Campeche, and that may allow for some modest re-intensification tonight and tomorrow.  But given the forecast calling for the center to hug the coast, the feeling is now that Ernesto would not be over the water long enough to return to hurricane strength before ‘his’ second Mexico landfall -- likely somewhere to the south of Veracruz.

The remnants of Florence still linger over the central Atlantic, but shearing winds and cooler waters will keep that system from re-developing.  Farther to the east, a very large tropical wave -- “Invest 92L” -- continues to show limited signs of slowly coming together.  We’ll likely be watching that disturbance for many days to come.

Tuesday, August 7, 2012

Hot & Humid, Scattered T-Storms

By Jay Grymes & Steve Caparotta

Highs returned to the low to mid 90°s as expected this afternoon with the Heat Index climbing above 100° before 1 PM.  We’ll admit to being a little gun-shy after Monday evening’s surprise storms, but we’ll go with isolated showers and a couple of rumbles of thunder later in the day, with any rain that does develop out of the way by or soon after sunset.  Look for partly cloudy skies through much of the night and into the morning, with Wednesday sunrise temps in the low to mid 70°s.
We’re calling for a 30% to 40% rain chances for both Wednesday and Thursday afternoons -- typical numbers for August given the heat and humidity.  Set rain chances on Friday at about 40% as well.  Look for highs in the low to mid 90°s on Wednesday, and low 90°s for both Thursday and Friday.
Keep highs in the low 90°s and ease back the rain chances slightly for the weekend, with a 30% rain chance on Saturday and only a 20% chance on Sunday as slightly drier air works its way into the lower Mississippi Valley.

As of 1 PM, Ernesto has been upgraded to a Category 1 hurricane -- the season’s second hurricane.  The current forecast still calls for Ernesto to landfall over the Yucatan tonight and then head west into the Bay of Campeche.  While it does appear from recent satellite imagery that Ernesto has eased a little north of his forecasted track, the shift is not sufficient to become a worry for the U.S. -- after entering the SW Gulf Ernesto is still expected to stay on a mainly west course and make a second landfall along the Mexico Coast between Veracruz and Tampico.

Elsewhere in the tropical Atlantic, remnants of Florence are still evident but are given virtually no chance for re-generation any time soon.  The other feature of interest is “92L,” a fairly substantial tropical wave in the eastern tropical Atlantic.  Although current conditions are deemed as only marginally favorable, it does appear that the environment could become a bit more conducive for development a few days down the road.  However, given its present location, there is no reason at this point to be alarmed.

Monday, August 6, 2012

Fairly Typical August Weather

By Jay Grymes & Steve Caparotta

Apparently much of the WAFB viewing area never quite got to the expected “convective temperature” -- this is the temperature at which the moist, low-level Gulf air mass gets enough lift from surface heating to build rain clouds. As of 2PM, there were some decent storms over SW Louisiana and coastal Terrebonne and Lafourche Parishes, but most of the WAFB viewing area was still rain-free. The same was still true at 3PM, and even at 4PM, there wasn’t much “popping” in our viewing area. Apparently some mid-level dry air kept a bit of a “lid” on the afternoon development. 

Any lingering thunderstorm threat should wind down fairly quickly later this evening as we remain under fair to partly-cloudy skies. Temps should slip to the low to mid 70°s for metro BR by Tuesday’s sunrise, and early-morning commuters may even run into a patch or two of light fog (but not enough to be an issue for the drive-to-work).

We’re going with 30% to 40% rain chances for Tuesday, Wednesday and Thursday. These will be the mainly-afternoon variety of showers and storms -- fairly typical August stuff. We’re still expecting some neighborhoods to reach the mid 90°s over the next couple of days, but we shouldn't have to deal with upper 90°s any time soon. In addition, it looks like we won’t be dealing with dew points in the upper 70°s to near 80° this week, which means slightly lower morning minimums and slightly less-oppressive afternoon heat. But don’t be fooled into thinking we’re in for a week of summer relief: it is August.

In fact, we’ll keep rain chances in the 30% to 40% range right through the weekend, with lows in the low to mid 70°s and highs in the low 90°s for the weekend as well.

In the tropics, Florence has all but collapsed over the last 24 hours. Shearing winds, dry air and a generally unsupportive environment has reduced Florence to a “post-tropical remnant low” according to the National Hurricane center (NHC), which implies a low that has lost the thunderstorm structure to be deemed a tropical cyclone. Although we may watch the remnants over the coming days, any re-development appears highly unlikely.

By contrast, after a prolonged run of fairly steady winds and pressure, T.S. Ernesto displayed some notable strengthening earlier today, but that intensification has leveled off this afternoon. Still the environment around Ernesto looks supportive for additional development and the latest projections from the NHC call for Ernesto to become a hurricane within the next 12-24 hours. In response to the apparent and forecasted intensification, as well as evidence of a jog to the west or NW today, the computer forecast guidance appears to be collectively easing a tad northward. Even so, Ernesto will likely make landfall near the Belize/Mexico border in the western Caribbean, then spend the better part of a day over land before emerging in the Bay of Campeche.

Admittedly, a northern shift will mean more time over the SW Gulf/Bay of Campeche, allowing for some re-intensification. But for the time being, a continued motion to the west or WNW is expected after entering the Gulf, which means no threat to U.S. interests.

Friday, August 3, 2012

More Action in the Tropics!

By Jay Grymes & Steve Caparotta

Heat and humidity today prompted the NWS to post yet another “Heat Advisory” for the majority of the WAFB viewing area ... the Advisory will be allowed to expire at 7PM, but it will still be uncomfortably warm well into the late evening.
Most of us just suffered through a hot-and-humid afternoon, but Titan9 Doppler did show a few t-storms developing in the viewing area, including two that became “severe” - - one over northern Terrebonne Parish and another extending over portions of Livingston and Ascension Parishes.  Today’s pockets of storms serve as a great reminder that even during relatively quiet weather days, isolated strong-to-severe storms can bubble-up almost any time during a summer afternoon thanks to the proximity of moist and unstable Gulf air.
The upper-air “Heat Ridge” centered over the Southern Plains that has been the driver for the excessive heat and series of advisories continues to contract and shift slightly westward, taking the “cap” off of our atmosphere.  We’ve seen the effects of the slow weakening of this “cap” with spotty t-showers on Thursday, isolated showers and t-storms today ... and our forecast calls for better rain chances for Saturday and Sunday as the ridge becomes less of a factor for the lower Mississippi Valley.
We’re thinking a 20% to 30% coverage for Saturday rains and a 30% to 40% rain chance for your neighborhood on Sunday.  Even with the scattered rains, we still expect highs to climb into the 90°s on both days, with a few areas possibly reaching mid 90°s on Saturday.  At the same time, the low-level Gulf moisture remains in place, keeping dew points in the 70°s with morning sunrise temps in the upper 70°s.
Keep scattered mainly-afternoon showers and t-storms in the forecast through the first few days of the upcoming work week as well.
All of a sudden, we’ve gone from one to three areas of interest in the tropics!  T.S. Ernesto continues to march across the eastern Caribbean and is still maintaining a quick-step forward speed of 20-22 mph.  After some brief weakening earlier in today, Ernesto has regained peak winds of 50 mph.  The NHC calls for very slow strengthening over the weekend, with Ernesto potentially becoming a hurricane in the next two to three days.  Ernesto’s forecast track has undergone only minor tweaks during the last 24 hours, and as of right now it looks like Ernesto will reach the southern Gulf sometime around the middle of next week.

A new area of interest has developed over the Bahamas today.  Labeled “Invest 91L” by the NHC, this disturbance remains poorly defined.  Very preliminary computer guidance suggests the 91L likely tracks to the NW or NNW towards Florida or possibly Georgia in the coming days.  We’re awaiting more model runs and updates, but for the time being we are not overly concerned about this system.
And lastly, a very healthy looking tropical wave in the eastern Atlantic (near the Cape Verde Islands) may be the precursor for our next ‘named’ system.  Although it offers no threat to land any time soon, it does send us a reminder that we are moving into the peak of the hurricane season.

Thursday, August 2, 2012

T.D. #5 Becomes T.S. Ernesto

By Jay Grymes & Steve Caparotta

Wednesday proved to be another in a run of hot and humid days, although clouds through much of the afternoon filtered the sunshine which slowed the rate of heating.  In fact, the cloud deck became so thick by the late afternoon that temps dipped back down into the 80°s for a number of locations.  Even so, temps around the metro area managed to climb to around 90°, and dew points in the mid to upper 70°s drove the Heat Index to 100° or more as early as 11AM.
The Southern Plains upper-level ridge continues to put a clamp on rain chances over the viewing area, but the eastern “edge” of the ridge continues to ease its way westward as the ridge contracts.  Over the past several days, we’ve been watching disturbances sliding around the northern and eastern edge of that ridge.  On Monday, most of the storms were rolling north-to-south through Alabama.  Yesterday, the storms tracked through Arkansas and Mississippi.  And today, while the main activity continued to run from Arkansas into Mississippi and western Alabama, Titan9 Doppler did pick up a few showers and a couple of t-storms along the Louisiana coast.
But for the vast majority of WAFB neighborhoods, Wednesday was just another hot-and-humid day.
We’re calling for spotty rains for Friday -- coverage for the WAFB viewing area at 20% or less -- with highs again returning to the low to mid 90°s.  The upper-ridge looks like it will continue to weaken and shift to the west during the weekend, allowing for better rain chances -- and a slight drop in daytime highs -- for both Saturday and Sunday.  We’re calling for 20% to 30% rain chances for Saturday and a 30% to 40% chance for Sunday.  We’ll keep scattered afternoon rains in the forecast for next week as well.

So what about Tropical Depression #5?  A ‘Hurricane Hunter’ aircraft  visited the storm during the afternoon and found winds sufficient for an upgrade, making T.D. #5 the fifth ‘named’ storm of the 2012 season: Ernesto.

Conditions around Ernesto remain a little ‘hostile’ and the forecast for the next 24 hours calls for only limited strengthening as Ernesto tracks to the west.  But once the tropical storm moves into the eastern Caribbean, there is some suggestion that conditions will become more favorable for the system to strengthen.  Indeed the National Hurricane Center (NHC) calls for Ernesto to reach hurricane strength by Monday.

Several long-range forecast models bring the storm into (or at least close to) the Gulf region sometime around the middle of next week.  As we said yesterday, there’s no reason to get to worked-up about that just yet, but the weekend would be a great time to sit down and evaluate your “readiness” should a storm come calling on Louisiana at any time in the next few months!

Wednesday, August 1, 2012

Still Hot; T.D. #5 Forms in Atlantic

By Jay Grymes & Steve Caparotta

Today’s HEAT ADVISORY will be allowed to expire at 7PM this evening, but not before many neighborhoods reached the mid 90°s.  Still, the heat did not seem quite as oppressive as what we experienced during Sunday, Monday and Tuesday afternoons.  But don’t be fooled: the very warm start to the day, the morning warm-up and dew points in the mid to upper 70°s had Heat Index numbers climbing above 100° before noon.
And that morning minimum of 80° for Wednesday is not only the “warmest” minimum of 2012, but the highest minimum at Metro Airport since August 2011!  Just how rare is a minimum in the of 80°s for Baton Rouge?  It’s only happened 22 times since 1930 (83 years), with the highest recorded minimum of 82° occurring only twice during those eight decades!  (An additional point: there were no minimums of 80° or more between 1930 and 1962!)

The upper-level “Heat Ridge” centered over the Southern Plains has kept us dry over the past couple of days and will continue to keep most of us hot-and-dry for the next few days.  We think that the ridge may weaken slightly and ease a bit westward over the next two days (Thursday & Friday), allowing for a slight chance of rain during both afternoons.  Earlier in the week we expected that ridge contraction and weakening to continue into the weekend, but some of the computer guidance now suggests that the ridge might re-strengthen from late Friday into Saturday, keeping a clamp on rain chances through Saturday afternoon and evening.
So for now, we’ll keep rain chances posted as “isolated” through Saturday, with a slightly better chance of rain on Sunday afternoon.  By Monday, the ridge weakens and shrinks enough to allow for scattered afternoon showers and t-storms, with scattered rains remaining in our forecast through the rest of the 7-day forecast.
A disturbance in the central tropical Atlantic -- about 800+ miles east of the Lesser Antilles -- has shown slow-but-steady organization throughout the day, prompting the National Hurricane Center (NHC) to ‘upgrade’ the disturbance to Tropical Depression #5.  Given its rate of development today, we wouldn’t be surprised to see T.D. #5 become T.S. Ernesto as early as tomorrow.  (Historically, roughly 9-in-10 Atlantic Basin depressions become tropical storms.)
Forecast guidance consensus takes T.D. #5 into the north-central Caribbean over the weekend, with slow-but-steady intensification.  Although intensity forecasting is far more uncertain than forecasting direction, there is a modest (far from unanimous) consensus among the intensity models suggests that the system could become a moderate-to-strong Ernesto in 4 to 5 days.

In any case, it is far too early to consider this storm as a Louisiana threat.  Even if the storm continues on its current directional trend and forecast, it wouldn’t reach the southern Gulf before sometime close to the middle of next week.  So don’t get too alarmed at this point ... but now is a good time to assess your family and business ‘state of preparedness.’
And don't can track T.D. #5 and any other tropical systems in our Hurricane Tracking Center: