Thursday, August 28, 2014

Good Rain Chances for the Holiday Weekend

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- Scattered rains for Friday afternoon, wetter for Saturday & Sunday 
- still waiting for 98L to move inland into Texas

We’ll start with a look again at 98L, that area of disturbed weather spinning east of Brownsville. It has been slow to move but appears to have finally moved onto the Texas coast as of the mid-afternoon. Although we’re still seeing some storms associated with it over the western Gulf, development chances for a tropical cyclone now appear to be “zero.” However, given the time of year and the warm Gulf waters, we’re not ready to declare 98L officially dead until it is fully inland later this evening.

It has been another mostly-dry day for the WAFB viewing area with rain activity occurring well to our west. However, an east-to-SE flow has become re-established over the viewing area today, bringing in more Gulf moisture. The enhanced humidity, working with daytime heating, popped a few afternoon showers and t-storms, but today’s sun/cloud mix helped slow the mid-day warm-up. What rain is out there this afternoon will subside into the evening, with partly-to-mostly cloudy skies expected overnight and into Friday morning.

Friday’s morning commute should be a dry one -- with the exception of a possible shower or two closer to the coast. Plan on Red Stick temperatures in the mid 70°s around sunrise. Temperatures should climb to 90° or above for most WAFB neighborhoods before Friday’s scattered afternoon showers and t-storms knock back the daytime heat. We’re calling for a 50-50 rain chance on Friday afternoon for the viewing area -- so be ready to hit some pockets of rain during the Friday evening drive home. 

Friday’s rains will again subside into the evening, but we’re going to carry isolated rains in the overnight and early Saturday outlook. By mid-day Saturday, we’re going with widespread rains for our forecast, setting Saturday’s rain chances at 70% or better. These probably won’t be all-day continuous rains, but be ready for on-and-off showers and storms throughout the better part of the day. Saturday’s wet weather should keep daytime highs in the 80°s rather than the 90°s. unfortunately, the next day doesn’t look a whole lot drier either: we’re calling for a 60% rain on Sunday with highs near 90°.

For Monday, Labor Day, we’ll ease back on the rain chances to around 40% -- an improvement over the weekend numbers but still the scattered afternoon variety of Louisiana summer weather. And for next week’s Tuesday-thru-Thursday window, we’re keeping rain chances in the 30% to 40% range for each day.

Elsewhere, ‘Category 1’ Cristobal shows no signs of weakening just yet; in fact, there remains a chance that Cristobal could actually get a little stronger before ‘he’ finally begins his transition to a non-tropical system in the North Atlantic. We’re still watching a broad west-to-east oriented low-pressure belt stretching from the central Caribbean to the tropical Atlantic east of the Lesser Antilles. While there is no imminent threat for development, this area needs to be watched as it moves to the west in the coming days. Some of our computer guidance is hinting at potential development early next week over the western Caribbean or southern Gulf. And lastly, although the NHC experts are less “bullish” about it than they were just a day or two ago, they are still watching a tropical wave about to enter the eastern Atlantic off of West Africa.

And then there’s football.

For south Louisiana high schools, be ready for a little rain during Friday night’s jamborees, although we expect the showers to steadily subside through the evening. As for Saturday’s big college contests in Houston, Lafayette and Hammond, afternoon tailgaters will want to have the rain-gear on the ready wherever they are. For the Tigers in Houston against Wisconsin, the good news is that the ‘lid’ will be closed on Reliant Stadium for the match-up with Wisconsin (8pm kick-off). But for the Jaguar Nation visiting ULL in Acadiana (6pm) and for the SLU Lions fans enjoying their home opener at Strawberry Field (7pm), scattered rains are likely to still be dotting the south Louisiana landscape at “first whistle” and lingering for much of the respective first halves.

Wednesday, August 27, 2014

Rains Returning to the Forecast

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:
- rain chances rising into the weekend
- still eyeing the disturbance in the western Gulf

For most of us, today was another relatively quiet weather day, with a prolonged run of NE to easterly breezes thanks to the circulation around the low-pressure area in the Gulf. After a morning start in the low 70°s for the Red Stick, most WAFB neighborhoods climbed into the low 90°s for the afternoon, but rains were fairly limited and the humidity was quite tolerable for an August day.

Of course, most of the local weather attention remains focused in the western Gulf. Admittedly, the area of low pressure tried to ‘kick up its heels’ overnight with another round of convection popping up in the early morning. The low-level circulation was (and is still) evident, but throughout most of today the main storm energy with this system remained to the north and east of the low-level spin. As of this afternoon, the National Hurricane Center (NHC) remains unimpressed with the disturbance -- listing it with only a 20% chance for development in the next two days. However, the NHC did concede that it deserves attention, dubbing it “Invest 98L” and scheduling today’s visit by aircraft. 

So, the real question for 98L: will it stay out over the water long enough to get its act together and earn tropical cyclone classification (as a depression or tropical storm)?

Well, there is no question that the Gulf is ‘warm’ enough to support intensification and the mid-level shear has appeared to relax a little today. Given the time of year, we won’t rule out a brief upgrade to depression strength, especially if 98L slows its westward movement. However, “space is limited” for the system -- if it doesn’t slow to a crawl or stall soon, it will be over the Texas coast before you know it. Regardless, high pressure to our north should keep 98L well to our south and southwest and west-bound into Texas. And for “droughty” central Texas, a dose of tropical rains would be welcomed.

For us, the drier pattern we’ve enjoyed is coming to a quick end. Winds will start to swing back around from the SE by mid-day Thursday, pumping Gulf moisture back into the viewing area. And as we head into the weekend, the Gulf moisture looks like it gets a bit of a boost (added lift) from both the north and the south. An upper-air trough will be sliding west-to-east across the central U.S. this week, breaking down the high-pressure ridge that has persisted over the Southern U.S., while northbound energy coming out of the Caribbean heads towards the central Gulf Coast by the weekend. 

In short: a rainmaker’s sandwich.

For Thursday and Friday, we’ll call for morning lows in the BR metro area in the low to mid 70°s, with afternoon highs in the low 90°s. Set afternoon rain chances at about 30% under an afternoon sun/cloud mix for Thursday, then 40% for Friday afternoon and early evening.

At this stage, the Labor Day weekend is shaping up to be a fairly soggy one. Showers and t-storms are likely for Saturday, with rain chances on Sunday at 50% or better. The rain and clouds should keep most at or below 90° over the weekend, but the trade-off could be localized nuisance flooding. (Note: localized .. not widespread)

With a little luck, Monday should be a bit better, but even then we’re carrying scattered afternoon showers and storms in the outlook.

Elsewhere in the tropics, ‘Category 1’ Cristobal is holding strong but is no threat to the U.S mainland nor to Bermuda. While Cristobal will still be on the weather maps this weekend, ‘he’ is headed towards the northeast and will be tracking over cooler Atlantic waters. A weak tropical wave about 400+ miles east of the Lesser Antilles (formerly labeled as “Invest 97L”) offers no serious threat for development, at least not over the next several days. (We will keep an eye on this wave, however, as some of the guidance suggests that it might re-fire over the western Caribbean or southern Gulf. Lastly, the NHC is also watching a healthy tropical wave about to enter the eastern Atlantic from the African continent, but it is simply too far away to worry about.

As for the Saturday night football outlook, whether you are headed to Houston for LSU’s match-up with Wisconsin (8pm kick-off), following the Jags to Lafayette to take on the Ragin’ Cajuns (6pm kick-off) or catching the SLU Lions at home in Hammond (7pm) against Jacksonville, fans will want the raingear handy. We’ve got scattered-to-likely rain chances at all three locations, especially during the afternoon tailgating hours.

Tuesday, August 26, 2014

Staying Mainly Dry on Wednesday

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- increasing rain chances through the week
- watching a weak disturbance in the northern Gulf
On this anniversary of 1992’s Category 3 Andrew landfall in Louisiana, it’s a good time to stop and consider: are you ready if something tropical pops-up and threatens us in the coming weeks?  Louisiana has been ‘hit’ by nearly three-dozen hurricanes in the past 100 years.  A look at the Louisiana history books shows us that since 1900, the 4-week period from August 25 through September 21 (28 days) is extremely active for the Bayou State, accounting for 16 hurricane ‘hits’ including 6 ‘major’ hurricanes (Category 3 or greater).  That’s nearly half of all the hurricanes to hit the Louisiana since 1900 and half of all the ‘majors’ to make landfall here.
Are you prepared?  “Get a Game Plan!”
We enjoyed a fairly decent August day today.  Not only did many of us miss out on the 90°s this afternoon, but with dew point temperatures running in the 60°s to low 70°s for much of the viewing area, we put some “weather distance” between us and the oppressive heat-and-humidity we suffered through last week and this past weekend.  But it is still August … and it is supposed to be hot … and the 90°s will return.
As you’ve probably heard, we have an area of action in the northern/northwestern Gulf that we’ve been watching for the past couple of days.  There are signs of a cyclonic spin but there is no clear organization at the surface and most of the regional convection (t-storm activity) is located north and east of that spin.  Given its current state and the disturbance’s expected movement towards the west, it looks as though it will reach the Texas coast before it can get organized.  That’s a big reason why the National Hurricane Center has it listed at just a 10% chance for development over the next two days (about all the time it will have over water if it doesn’t stall).  Frankly, we think that 10% may be a little on the low side and we must always be wary of anything spinning over the very warm Gulf waters at this time of year.  But the way it looks to us, no matter what becomes of this, it is not going to be a tropical problem for Louisiana -- possibly a rainmaker for some of the southwestern parishes, but that’s about it.
That same northern Gulf low is partly responsible for our lowered humidity today, with its counter-clockwise spin pulling air into our region from the ENE and NE.  But as we head into the next couple of days, we’re expecting a return of a more southerly flow over the WAFB viewing area.  That means back to our summer Gulf humidity: making it a bit stickier during the day, a little warmer and muggier at night, and increasing the afternoon rain chances as well.
We’ll stay with highs in the low 90°s through Friday, with morning minimums back into the mid 70°s for most of us by mid-week.  We’ll go with a 20% to 30% rain chance for Wednesday, a 30% to 40% chance for Thursday, then up it to 50% or better for Friday, Saturday and Sunday.  Sadly, it looks like half of more of us will be dodging the rains each day through the Labor Day weekend.
Elsewhere in the Atlantic, Category 1 Cristobal will continue ‘his’ slow movement to the north and NNE for the next day or so.  All indications are that Cristobal will miss Bermuda as ‘he’ accelerates on his way towards the cooler waters of the North Atlantic.  The National Hurricane Center (NHC) is also eyeing a tropical wave located roughly 800 miles east of the Lesser Antilles.  However, development appears rather unlikely over the next couple of days, at least, with the NHC only posting a 20% chance for development through the next five days.

Sunday, August 24, 2014

Sunday (8/24) Tropical Update

Here is your tropical update for South Louisiana for August 24th, 2014.

The 3rd named storm of the 2014 Atlantic hurricane season formed over the weekend.  Tropical Storm Cristobal developed around the Bahamas where it remains this Sunday evening.

T.S. Cristobal remains a very poorly consolidated tropical system.  Maximum sustained winds remain at 45 mph.  T.S. Cristobal is having hard time getting aligned vertically in the atmosphere.  The lower level and mid and upper level circulations are displaced.  Until they align Cristobal will be unable to truly strengthen.  T.S. Cristobal is also dealing with some wind shear although the shear is not significant enough to limit some development.

The continuing good news for the Gulf Coast States is that T.S. Cristobal is moving away from the Gulf and also the East Coast of the United States.  The official National Hurricane forecast track calls for T.S. Cristobal to slowly drift north over the coming days and strengthen some.  It could reach hurricane status Thursday morning.  T.S. Cristobal is being steered by a weakening high pressure system to its east and west and a trough to its north.  The consensus is that the trough will help guide this system out over the open waters of the Atlantic away from land.

The weather guidance model forecasts are also becoming a little better aligned.  We no longer see any models suggesting a Gulf of Mexico track.  The biggest disagreement is how fast this system moves out to sea once it makes its northeastward turn late Wednesday.

A new tropical wave has developed in the Central Atlantic this afternoon.

The wave has been given very minimal chances for immediate development.  Dry air and high wind shear should keep this wave very disorganized and weak over the next several days.  Weather guidance models show a due west track at about 15 mph for the next couple of days.  Only the very aggressive Canadian Model shows some development of this system over the next 5 days.

10 DAY OUTLOOK: ***(DISCLAIMER: 10 day outlook is a long range forecast and can change rapidly and should NOT be accepted as "gospel" truth but only a small possibility and something to keep an eye on over next several days.)***
Long range model guidance does appear to show things becoming "a little" more active across the intertropical convergence zone.  That is the central Atlantic just off the coast of Africa.  This is typical time of season that this area of the tropics becomes a little more active, so that's not out of the norm.

The image above is the GFS model 10 days from now.  We see the tropical wave currently in the Central Atlantic that is given a minimal chance of development over the Bahamas as a weak tropical wave.  But another system out to the west over the central Atlantic does look more impressive.  This would appear to indicate a tropical depression or weak tropical storm.  We also see a few more waves moving off the coast of Africa (indicated by the solid clump of rain from the African coast to the west).  Keep in mind this is 10 days from now and model guidance accuracy this far out is highly suspect.

Friday, August 22, 2014

Upper 90°s This Weekend?!

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:
- getting even hotter over the weekend
- only a handful see cooling showers on Saturday & Sunday
- 96L still not much better organized
So today makes it four consecutive days at 95° for Metro Airport (BTR), and all indications are there is more of this heat to come.  In fact, ‘hotter’ is the forecast, with upper 90°s expected through the weekend and possibly on Monday as well.
That would mean seven consecutive days at 95° or above for BTR.  You bet that’s hot: we haven’t seen a run that long in two years (June 2012).  But it’s not rare either: this would be the 9th time in the past ten years with highs of 95° or more over a period of seven or more days.  In fact, it happened three times in the summer of 2011, including a 23-day stretch at 95° or above in August 2011.
The upper-level ridge (sometimes called a “heat ridge” in the summer) will remain in place through the weekend, adding to the daily heat-up by inhibiting the development of rain clouds and producing “sinking” air from above.
For some, you may be thinking, isn’t it cooler up above the surface?  Yes -- that’s why tall mountains can maintain snow cover at their tops even through the summer months.  So why does sinking air from above add to the daytime heating at the surface if it is cool enough to allow snow on mountain tops?  True, it is cooler where it starts, up at those elevations.  But as the air parcels from above start to sink, they are moving from a levels of lower pressure (the air pressure is lower is you go higher and higher up in the atmosphere) to levels of higher pressure.  For the atmosphere, the highest pressure is always at the Earth’s surface.
In other words, when air descends, it is moving into levels of increasing pressure: it is being compressed (squeezed) by the air around it.  As you may remember from your school days, as pressure increases, so does temperature.  In effect, the cool air from above warms considerably as it descends from the increasing pressure.  Meteorologists call this “adiabatic warming” and it is impressive: descending air will warm more than 5°F for every 1000 feet, or nearly 30°F for one mile of descent!  (Now that doesn’t mean that we are getting warmed by 30° from the sinking air!  But the descending air can easily add a few degrees to the already ‘hot’ surface temperatures.)
For the local forecast, we won’t say “no rain” for the weekend but we’re going with rain chances at 20% or less for both Saturday and Sunday -- in fact, it’s looking very spotty for Sunday.  What’s more, Sunday shapes up to be the hottest day of our current run with highs for just about everyone in the upper 90°s - - some neighborhoods may get awfully close to 100°!  Thankfully, by late Sunday into Monday, the overhead upper-level ridge begins to relax a tad, allowing for rain chances back to around 30% or so for Monday afternoon, although Monday's highs will still hit the mid to upper 90°s around the viewing area.  Into Tuesday and mid-week, the ridge retreats enough to get us back to something a little more typical  for August: scattered afternoon rains with highs in the lower 90°s.
As for morning lows, plan for more mid to upper 70°s likely for the next several days.
And now for Invest 96L … The National Hurricane Center fixes the main surface low-pressure zone north/northeast of Hispaniola and on a path towards the southern Bahamas.  96L has shown a bit more convection today, but nothing that clearly says that it is demonstrating a definitive center.  Indeed, as of this afternoon, there appear to be at least two or three places -- including one patch still in the Caribbean -- that could become the system’s core in the next 24-48 hours.  Remember, until we have a clear-cut center, forecasting the “where to” remains tricky.
For the time being, the consensus of model track forecasts keeps 96L (or possibly T.D. #4 or even T.S. Cristobal) in the western Atlantic, with the system being tugged northward by a developing trough near the U.S. East Coast in the next couple of days.  So, while we are not be ready to say that a visit to the Gulf is completely "off the table,” current signs are mainly good news for Louisiana and Gulf interests.

Thursday, August 21, 2014

Hot August Weekend Ahead!

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- heat continues for Friday & the weekend
- rain chances drop to less than 20% over the next three days
- lots of interest in the tropics

For the second day in a row, afternoon thunderstorms were more widespread than anticipated. The upper-level ridge that we’ve been talking about for days remains in play, but a small, mid-level low has been working with our warm-and-unstable Gulf air and sea-breeze set-ups to produce some afternoon fireworks. As before, the action winds down as the sea-breeze departs and the daytime heating fades. We’ll go to fair to partly cloudy skies overnight and into Friday morning with sunrise lows in the mid 70°s for metro Baton Rouge.

And like yesterday, while the storms and clouds provided some heat relief, Metro Airport (BTR) still managed to hit 95° before the weather produced a marked temperature drop. That also makes three days in a row with highs of 95° for BTR -- that’s the three hottest consecutive days for BTR since early July of 2012.

Can we expect another round of scattered t-storms for Friday afternoon? Given the coverage of storms for yesterday and today, we won’t rule it out, but we do believe that the mid-level low that generated today’s action will be just about gone -- we’ll call for isolated t-storms and rain chances at 20% or less for Friday afternoon.

We’ve got it even “drier” for Saturday and Sunday, calling for spotty rains at best on both days. But what we can expect is even more heat for Friday and the weekend, with highs in the mid to upper 90°s for just about everyone for all three days.

Heading into next week, the upper-level ridge will begin to relax a bit, allowing for more clouds, better rain chances and a drop back into the low 90°s for highs.

So what about the tropics, specifically Invest 96L? A hurricane hunter aircraft found winds of tropical-storm force in the vicinity of the tropical low, but the structure of the disturbance - - including a lack of convection (thunderstorms) near the estimated area for the surface low - - is too ragged for an upgrade to tropical depression status. However, the National Hurricane Center does give 96L a 50% chance for that upgrade over the next two days and a 70% chance over the next five days. 

This is not a time to drop your guard or stop those early preparations, and it is still too early to make definitive claims about the ultimate path that this tropical system will take. However, most of the latest computer analyses suggest that this system will remain in the Atlantic, regardless of its intensity in the coming days.

By the way, what is an “Invest” anyway? The term "Invest" is assigned to a tropical wave/disturbance (an area of disturbed weather, a cluster of thunderstorms) that is thought to have some potential for development into a tropical cyclone (a tropical depression or stronger). The term is shorthand for “investigation (investigative) area.”

In the Atlantic Basin, tagging a disturbance as an Invest signals that the National Hurricane Center is formally monitoring the area and is ready to begin the collection and evaluation of meteorological data associated with the disturbed area, as well as initiate the running of computer models on it. The Invest designation also alerts cooperating agencies (government and academic groups) to begin data processing in earnest.

Officially, designation as an Invest does not mean that the tropical disturbance has an increased likelihood for development, but it is a clear sign by the NHC experts that they think the area has at least some potential.

Invests are numbered from 90 to 99, and labeled with an “L” for disturbances in the Atlantic Basin. (By comparison, an “E” is used for Invests in the eastern Pacific). Given this naming scheme for Invests, you can see that during an ‘active' year, there could be two or more “90L” Invests before the season ends. Keep in mind that over the course of a tropical season, we could see as many as 50 to 70 (or more) tropical waves over the Atlantic, although only a small proportion of those earn Invest designation.

Take this season for example: we are currently watching 96L, the sixth Invest of the season. Yet only three have become tropical cyclones: hurricanes Arthur & Bertha, and between them, Tropical Depression #2.

Wednesday, August 20, 2014

Staying Hot into the Weekend

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- getting even hotter in the next few days
- tropics are becoming more lively

The outlook for the next couple of days remains generally unchanged: upper-level ridging settles over the lower Mississippi Valley, knocking rain chances down to less than 20% for most of the WAFB viewing area through the weekend. In addition, it means less cloud cover allowing the sun to heat things up even more and helping to drive maximum temperatures into the mid to upper 90°s for most WAFB neighborhoods. Yes, it’s still shaping up to be the ‘hottest’ stretch of days of the summer (at least so far.)

For the BR metro area, we’re calling for muggy mornings with sunrise temperatures in the mid to upper 70°s through Sunday. For the afternoons, temperatures in the 90°s throughout the entire afternoon for most neighborhoods will combine with Gulf humidity to drive Heat Index readings into the 100°s for runs of as much as 6 hours or more for many locations. And rain chances? Only a very few neighborhoods will be lucky enough to get a cooling shower and a brief break from the otherwise near-relentless daytime heat.

Be careful if you are expecting to spend extended time outdoors this weekend. This kind of heat sneaks up on you, especially if you are not accustomed to it. Emergency medical experts note that heat-related calls often increase over the weekends -- people (adults & youngsters) that were indoors during the week (at work and/or at school) are more likely to be outside during Saturday and Sunday, making them more prone to heat exhaustion (or worse).

The upper ridging will start relaxing by late Sunday, allowing daytime temperatures to drop a few degrees while also allowing for better afternoon and early evening rain chances by Monday through next week.

Lots of attention turning towards the tropics … what was a pair of tropical waves in the tropical Atlantic has essentially merged into one bigger tropical ‘blob’ east of the Lesser Antilles. As of 2pm, the National Hurricane Center (NHC) is giving the broad disturbance -- labeled Invest 96L -- a 50% chance for development (becoming a tropical depression or tropical storm) over the next 2 days with that likelihood up to 60% over the next 5 days. 

Computer model remain rather “mixed” in terms of the future of 96L for direction, forward speed, and intensity. But that’s no surprise given the current lack of organization. The general consensus suggests movement towards the west-NW then NW over the next 4 to 5 days, taking it somewhere in the vicinity of Cuba or the Bahamas. But remember: that is not a forecast!

Let’s not get too concerned yet, but also let us keep in mind that a “system in the Gulf” is still definitely on the table. However, should this system develop and get into the southeastern or southern Gulf, it wouldn’t happen before sometime next week. That gives you time to revisit your family and business preparedness plans to make sure you are ready for the “peak” of the Hurricane Season.