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WU - Masters/Henson post

Posted by cypresstx on 9/28/2017, 2:57 pm

Maria and Lee On the Way Out; New Tropical Depression Possible near Florida

Bob Henson    September 28, 2017, 12:39 PM EDT

Watching the waters near Florida this weekend for new development

An area of disturbed weather extending from the northwest Caribbean across central Cuba and into the Bahamas on Thursday morning was associated with a broad trough of surface low pressure interacting with an upper-level low. This disturbance will move northwards through Saturday, when it will interact with a cold front pushing south across the Florida Peninsula. A small non-tropical surface low pressure system is expected to form by Saturday in the waters a few hundred miles off the east coast of Florida-or less likely, just off the west coast of Florida-and this low will have the potential to become a tropical depression over the weekend. The Hurricane Hunters are on call to investigate the system on Saturday afternoon, if necessary.

About 40% of the 70 members of the 0Z Thursday GFS and European model ensemble forecasts predicted development of a tropical depression in the waters surrounding Florida by early next week. None of these solutions had the system reaching hurricane strength, though. A strong ridge of high pressure will build to the north of the low by Sunday, forcing it to move westward. Wind shear over the system will mostly be moderate through Sunday, then likely rise to the high range by Tuesday, squelching any further development. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odds of tropical cyclone development of 20% and 40%, respectively. The main threat from this system will be heavy rain, and NOAA was predicting 2 - 4" of rain for most of South Florida over the week.

Keeping a long-range eye on the Caribbean and Gulf of Mexico

Conditions in October and November may end up quite favorable for Atlantic tropical cyclone development, especially in the Caribbean, which is a climatological hot spot late in the season. Sea surface temperatures in the Caribbean are substantially above average (1-2°C), and long-range models are calling for below-average surface pressures during October in the western Caribbean, which signals a higher-than-usual chance of tropical development. Moreover, we are currently in a La Niña-like pattern-with cooler-than-average sea surface temperatures (SSTs) already present in the eastern tropical Pacific-and this may help keep wind shear in the tropical Atlantic below average.

Both the GFS and European long-range models are suggesting the potential for a tropical cyclone developing in the Northwest Caribbean or eastern Gulf of Mexico somewhere in the 7- to 14-day period. In an outlook published on Tuesday, NOAA/NWS Climate Prediction Center (CPC) highlighted a moderate risk of tropical cyclone formation in the Oct. 4 - 10 period across the Northwest Caribbean and southern Gulf of Mexico. An atmospheric Kelvin wave located in the eastern equatorial Pacific this week will be moving toward Central America, favoring upward motion, according to CPC.

If a tropical cyclone does develop, it could end up being a slow-moving one, as a massive, summerlike upper-level ridge is expected to develop across the central and eastern U.S., blocking any quick movement toward the north (and likely bringing record or near-record October heat).

Dr. Jeff Masters co-wrote this post.


In this thread:

tropical cyclone formation potential - cypresstx, 9/27/2017, 8:04 am

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