Friday, August 16, 2013

Weekend Weather Hinges on Gulf Disturbance

By Jay Grymes & Steve Caparotta

Not a bad day today and we think Saturday shapes up to be much the same.  Admittedly, most of us missed out on the upper 60°s we forecasted for this morning’s start -- the air just didn’t get quite as cool and dry overnight as we had expected.  Still, most saw wake-up temps near 70° with Friday afternoon highs around 90°. 
A weak, meandering front continues to linger along the Louisiana coast.  It provided just enough lift to fire off a few showers and a couple of t-storms this afternoon and we can expect the same for Saturday.

Saturday will start off with fair to partly cloudy skies and sunrise temps in the upper 60°s to around 70° for metro Baton Rouge.  And like Friday afternoon, Saturday afternoon will be mainly dry with “comfortable” dew points running in the 60°s under partly cloudy skies and highs topping out around 90°.  No complaints for mid-August weather here along the Gulf Coast.
For now, we are going with scattered, mainly-afternoon showers and a few t-storms for Sunday, with scattered rains for Monday and Tuesday.  However, we admit to limited confidence in the Sunday-through-Tuesday forecast as the outlook for those days is largely dependent upon developments over the western Gulf.
Okay, so what about the low in the Gulf?
With some of the mid-day model updates available, the “smart money” goes for landfall along the TX coast in three days or so possibly as a low-end tropical storm (T.S. Fernand).  However, we still don’t have anything even close to a consolidated system as yet.   While there is a low-level spin evident to the west of the Yucatan, any significant convection is currently 100-150 miles or more to the ENE of that surface spin.  A look at the satellite loops confirms that the low-level spin is west of the Yucatan while the convection is north of the peninsula.

The convection (t-storm activity) to the ENE of the surface low is associated with an upper-level low -- arguably a potential nemesis for a tropical system in its pre-depression stage, especially when positioned to the east or NE of the low-level spin.  Now, if the convection can link up with the low-level spin without destroying it, then maybe something starts to organize over the weekend.  But we don’t see the convection merging up with the spin very quickly … nor do we expect the low-level spin to move much in the next day or two.
So, a ton of uncertainty remains.  One possibility, although not high on the list of real options, is that we get a surface center re-location, or more likely, a new low-level spin develops closer to the present convection envelope.   Another possibility: the upper-low disrupts the surface spin and 92L heads to the history books.
Could Louisiana still see a tropical storm landfall out of all of this?  For now, we’re saying that chances are well below 1-in-5 that 92L becomes Fernand and heads our way.  The latest run of our in-house 'Precisioncast' (RPM) does bring some part of the system toward the Louisiana coast on Sunday. IF that were to happen, Sunday would be quite a bit wetter than currently indicated in our forecast, but we don't expect winds or surge to be much of an issue.

Elsewhere in the tropics, the National Hurricane Center is still tracking Erin, now downgraded to a tropical depression (TD).  The official forecast keeps Erin at TD strength through the coming days but it is looking less likely that Erin will be a threat to the U.S., the Bahamas or the Caribbean.  Even if Erin maintains ‘her’ tropical characteristics through the coming week, the extended-range outlooks suggest that ‘she’ will start hooking to the north and remain over open water.

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