SPECIAL TROPICAL WEATHER OUTLOOK FORECAST SYNOPSIS…ISSUED APR. 23, 2017…4:40 P.M. EDT

Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.
(T. F. “Storm” Walsh III)

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Good evening everyone!

First, I am still having a hard time digesting that “Arlene” should have been named. Now, my “colleagues” at the NHC are the “official experts” in the subject.  However, I wish to point out some of “my” observations regarding Arlene.  In my humble opinion, I believe she should have been kept “sub-tropical” at best.  Yes, it had a warm core, however based on the SST’ at the time of designation, the SST was only 19.0C (66F).  This is hardly sufficient to perform the true tropical process of maintaining and strengthening a warm core.  Pretty much what allowed for a storm to develop, was when the process began, SST’s were 21C (70F).  Just barley enough to allow for the baroclinic low to transform to subtropical.  In this case, the SST’s were warm enough to aid in warming the “core”, as the atmosphere surrounding the low was colder in relation to the SST’s, as well as colder mid and upper level conditions.  This produced a good enough lapse rate to allow for shallow, to moderate convection at best, to develop in two bands just away from the center, which in archived satellite loop imagery waxed and waned.  The limited convection that was present, was maintained due to the difference in temperature between the sea and the surrounding atmosphere.  Based on the NHC’s own criteria, classification to tropical cyclone status requires organized, “DEEP” convection to be maintained for a minimum of 12 hours, around or near a well defined center of circulation.  Review of IR satellite loop imagery may suggest that the moderate convection SW and NE of the center, was brief lived.

CIMSS SATELLITE BLOG (CLICK FOR ANIMATIONS)

I also noted, that during the short life of the storm, winds in the upper levels of the atmosphere remained cyclonic, or counter-clockwise, which meant, there was no outflow channel aloft, to evacuate air in the upper layers, from the rising air coming in at the surface.  A tropical storm and hurricane need outflow at the top of the storm, in order to take in more warm air at the surface, and in turn, strengthen.  This was not the case with Arlene.

Review of satellite loop imagery revealed (at least to me anyway) that the cloud pattern was not that of a purely tropical system.  It resembled more of a storm embedded in a cloud pattern of the baroclinic low that was situated to its west.

Maximum winds were still noted in a band removed from the center of circulation, which is classic of subtropical systems, albeit the distance appeared less than 100 mi, the maximum sustained winds were not located around the center of the system, based on the last available Multiplatform Satellite Surface Wind Analysis.

MPSSWA

Anyway, it is what it is, and these are just some of my observations.

A weak area of low pressure is currently making its way NE across the Florida Peninsula from the GOMEX, and is noted in satellite imagery.

NOAA SSD SATELLITE LOOP IMAGERY

Analysis of the Global Models and the NAM Mesoscale model indicate models are in fair agreement of this low becoming better defined, and strengthening, ranging from 1000 mb to 990 mb.  This low is progged to move toward the NE during the next 24-30 hours, before merging with a baroclinic low IVO NC/VA.  It appears most of the weather will remain on the eastern portion of this system.  Models at the moment indicate a small area of 30-35 knot winds in a band on the eastern side of the system, skirting the coast of NC and VA,which will be an onshore wind.  Right now, it’s a little too early for me to determine whether or not this may try to acquire sub-tropical characteristics, however once merging with the baroclinic low, some heavy rainfall is possible over localized areas. 

GFS

CMC

NAM

GFS AND NAM 72 HOUR RAINFALL TOTALS

Approximately 48 hours into the forecast period, valid 12Z today, the low should begin to move off toward the NNE to NE, and begin to weaken.

I will be monitoring this area, and will try to have an update sometime tomorrow (time still to be determined)

Elsewhere, Tropical Storm formation is not expected.

Have a blessed evening!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
CoCoRAHS OBSERVER

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About palmharborforecastcenter

I am a Tropical Forecast meteorologist, providing hurricane forecasts during the Atlantic Hurricane Season. I retired from the U.S. Coast Guard in July of 2001. Meteorology became my passion in high school, and I have continued my educational background in meteorology since 1996, when I undertook the study of Tropical Meteorology. While working toward my degree, I had to unexpectedly withdraw from college due to my oldest sons medical reasons. I do however, meet the educational criteria of the AMS to be recognized as a meteorologist. Studies include, but are not limited to the Navy Aerographers Mate course, Naval METOC meteorology course, Meteorology 2010 Sophomore level course while attending St. Petersburg College, Clearwater, FL., Basic Forecasting course for operational meteorologists from Rapid WX, meteorology institute, a four month meteorological internship, and extensive research on numerous meteorological topics such as the MJO, NAO, satellite imagery interpretation, etc. I have been forecasting Tropical Weather (Tropical Storms and Hurricanes) since 1996, with my main client being three different Coast Guard Commands.
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5 Responses to SPECIAL TROPICAL WEATHER OUTLOOK FORECAST SYNOPSIS…ISSUED APR. 23, 2017…4:40 P.M. EDT

  1. Like you, I too have wondered about the “leap to get there first” by those at the NHC! Admittedly, they have some concerns about funding in the coming year and need to “be seen”, but that is no real excuse to jump in, when in the past they would have used reason not to have excited their followers to an almost state of panic. After 42 years of living on the Coast, I have learned to keep my insurance in play, “board-up” and leave “The Island” in plenty of time so I don’t have to fight those who wait till the last minute.
    Thanks Storm for your skills and knowledge.

  2. Pamela Iannacio says:

    Hay Storm

    I sent a donation but not sure if it went through never got a confirmation. could you check

    Thanks Pamela Iannacio

    On Sun, Apr 23, 2017 at 4:39 PM, WEST CENTRAL FLORIDA HURRICANE and SEVERE WEATHER FORECAST CENTER wrote:

    > palmharborforecastcenter posted: “Disclaimer: This site is not affiliated > with the National Hurricane Center, Hurricane Hunters, Storm Prediction > Center, or National Weather Service. ALL forecasts herein are the result > of my analysis, and I am solely responsible for the content. (T. F.” >

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