WESTERN CARIBBEAN DISTURBANCE FORECAST SYNOPSIS…ISSUED MAY 21, 2018…2:30 P.M. EDT

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(T. F. “Storm” Walsh III)

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Good day everyone!

An area of disturbed weather, associated with a surface trof of lower pressure, and upper level low is located in the W. Caribbean Sea.  The NHC has picked up on this, and has designated a LOW (20%) probability of cyclone development during the next 5 days.

NHC 5 DAY GRAPHICAL TROPICAL WEATHER OUTLOOK (LINKED…CLICK GRAPHIC FOR OUTLOOK TEXT)

This is the area I have been posting about, and what the global models have been “sniffing out” for the past 3 – 4 days.  ALL of the global models are still in agreement of a weak system developing, mainly after day 5 in the current forecast period.

A broad, low level circulation appears to be taking shape, noted in satellite loop images.  I have circled the area in question.

GOES 16 AND RAMSDIS SATELLITE LOOP IMAGERY (CLICK IMAGES FOR ANIMATION)

Based on the current wind shear pattern, upper level winds are not favorable for development at this time. 

CIMSS WIND SHEAR MAP

However, based on the current forecast wind shear analysis, upper level winds could become more favorable in about 5  days from 00Z yesterday evening, depending on which model is correct.  I generally prefer the GFS for the wind shear forecast, as it is generally correct up to a point.  However, until I see updated runs on the wind shear forecast, I am going to go out on a limb here, and favor the ECMWF wind shear forecast, for a few reasons.  The majority of the global modeling shows MSLP becoming lower as whatever this system may be, comes closer to shore.  The GFS has this coming across FL., and at the moment, I do not feel this is correct, which I’ll explain further on.  With the ECMWF, CMC, NASA-GEOS models indicating some slight strengthening prior to where these models indicate possible landfall, the scenario petty much coincides with the ECMWF shear forecast.  The ECMWF tends to indicate upper level winds may subside, and a small upper level anti-cyclone may begin to develop.  This would favor more of a chance for this low to develop.  I will have a better handle on the shear forecast as time goes on, so I can compare how the trend is in real-time shear, vs the model forecasts.

ECMWF WIND SHEAR FORECAST

Based on my analysis of forecast surface wind speeds, and distribution of the wind field, there could be the low probability of this attaining sub-tropical characteristics, and the low chance of a sub-tropical depression.  Regardless of development, this will be another east weighted system, with the wind field and precipitation limited to the north and eastern side of the system.

Based on the current steering layers map from CIMSS, this area of disturbed weather should be moving slowly toward the NW.

CURRENT STEERING MAP

I am going to reiterate here…exact path cannot accurately be determined at the moment, as model guidance is not being run at the moment.  Guidance will not be run, until a definite, well defined, closed low level circulation is detected.  The reason for this is, as you have seen with all the past model runs, the modes have been notorious for moving the “forecast path” back and forth.  This is because the models have no closed center to “latch” onto, and the heat energy associated with the system is spread out over a large area.  Once and if this becomes a solid, well defined low level circulation, the modeling will be better able to focus the heat energy more toward a “common center”, and have something to “see”  Thus, I’ll have a better handle on future track.  In the interim, based on analysis of the global models and current run of the forecast steering layers maps from the PSU e-WALL site, I am more inclined at the moment to favor a blend the ECMWF and CMC models, and I’ll explain why.  The GFS brings this northward, then over the FL. Peninsula, as does the FIM.  In my analysis of the forecast steering maps, should they be accurate, the steering flow is forecast to remain pretty close to what the CURRENT steering map shows which is previously posted, for the next 72-96 hours.  Thereafter, the flow is forecast to shift to more of a south-north orientation.  So, the bottom line for right now is, this “could” be in the central GOMEX, before it may turn NNW to due north.  I did not note anything that would suggest the forecast motion that the GFS is indicating.  For all intents and purposes at the moment, SHOULD this become a sub-tropical depression, or just remain a weak low, a “landfall could occur anywhere from the extreme W. FL. Panhandle, to W. Louisiana.  I should have a better idea on track once this comes through the Yucatan Channel.

ECMWF FORECAST

GFS

CMC

NAVGEM

FIM

NASA-GEOS


Regardless, the majority of wind and precipitation should be north and east of the “center”.

WPC 7 DAY TOTAL ACCUMULATED PRECIPITATION FORECAST

ECMWF 10 DAY PRECIPITATION TOTAL FORECAST

I will continue to monitor this area, and will update when I can.  Still unsure about my workdays and hours with the new job.

Have a blessed day!

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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