TROPICAL DEPRESSION 15 / POSSIBLE N. BAHAMAS / GOMEX DEVELOPMENT FORECAST SYNOPSIS…ISSUED SEP. 16, 2023…12:40 P.M. EDT

ALL forecasts herein are the result of my analysis, (to which you will see me at times, insert excerpts from various agencies due to the nature of the importance of the information) and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(T. F. “Storm” Walsh)

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I will reiterate, my forecasts are based on the available information at the time of analysis, and are only as accurate as the information analyzed and the solutions provided.  Keep in mind, if a forecast doesn’t exactly pan out, remember, the atmosphere is fluid in motion.  When models are being analyzed, that’s just one run, and I have to go with what is presented.  After that, models don’t update again for another 4 – 6 hours, so, what happens between that time is unknown, and forecast conditions can change slightly, to greatly.  This will have an effect on my actual forecast.

The following is my outlook forecast for the 2023 Atlantic Hurricane Season:
STORM W SEASONAL FORECAST
TOTAL NAMED STORMS: 14– 16
TOTAL HURRICANES :        5 – 7
MAJOR HURRICANES:        3 – 4

AVERAGE HURRICANE SEASON:
TOTAL NAMED STORMS: 14
TOTAL HURRICANES:         7
MAJOR HURRICANES:        3

SEASON TOTALS:
NAMED STORMS:          13
HURRICANES:                 5
MAJOR HURRICANES:  3

Given that the NHC has named at least 3, if not more, garbage systems, I had to increase my seasonal forecast slightly.

The following are the storm names for the 2023 hurricane season.  As each storm is named, they will be colored in red in order to keep track of the used names in the list:

Arlene Bret Cindy Don Emily Franklin Gert Harold Idalia Jose Katia
Lee Margot Nigel Ophelia Philippe Rina Sean Tammy Vince Whitney

Greetings everyone! 
As a reminder, when forecasting tropical systems, if there are numerous systems to deal with, I always update on the systems that may present an impact or threat to either the U. S. or the Caribbean islands.  Anything far out in the Atlantic or something that may re-curve, take a lower priority as there is more time to deal with them.

Tropical Depression 15 has not changed much this morning as far as organization.  Based on satellite loop imagery the circulation is broad and just south of the convective activity.  The system is currently under some SELY shear, which would account for the system being not fully vertically stacked.  As of the 11:00 a.m. advisory from the NHC, the following was available on Tropical Depression 15:
11:00 AM AST Sat Sep 16
Location: 19.7°N 46.2°W
Moving: NNW at 18 mph
Min pressure: 1006 mb / 29.71  in
Max sustained: 35 mph
WEATHERNERDS GOES 16 HURRICANE TD 15 LOOP IMAGERY

Tropical Depression 15 was moving toward the NNW.  Based on current steering, analysis of 500 mb geopotential height forecast maps, and interactions with some other weaknesses in the ridging due to Margot and LEE.  As Margot moves out, ridging will have the tendency to build back briefly, before the another mid level trof moves off the eastern U.S., and creates another weakness which should pick up the system and cause it to re-curve.  Although the forecast pattern is somewhat similar to Florence back in 2018. where Florence came back and hit the U.S., global ensemble models and ATCF track guidance seem to have been fairly consistent on future track and are fairly tight in the guidance.  Based on this, I agree currently with the NHC forecast track:
VARIOUS GUIDANCE FORECASTS



NHC FORECAST TRACK
Maximum sustained winds were 35 mph.  For now, the intensity forecast is going to be a little tricky.  Though the depression is experiencing some shear at this time, based on the previous analysis of wind shear from CIMSS, and the most current one, the radial shear pattern has come closer to the center of the system.  This could be an indication that shear may be beginning to lessen.  It is noted that an established outflow pattern is over the system.  Conditions are forecast to remain favorable for further development, based on analysis of forecast shear, PWAT, mid level RH, and 200 mb streamline maps, although a slight difference in the 200 mb pattern is noted during the first 48 hours between the ECMWF and GFS models.  Future intensity is going to depend on whether or not the depression can develop a tighter circulation and stronger core.  The slower this occurs, the slower the rate of intensification.  Should the depression begin to come together more quickly, some brief rapid intensification could occur given the forecast conditions, and high enough OHC in the forecast track.  This could begin in about 36 – 48 hours, and is reflected in the NHC intensity forecast to which I agree with, based on the immediate uncertainty of intensification.  IF the system gets its act together quickly, I cannot rule out a minimal CAT 3 hurricane at the strongest point:
NHC INTENSITY FORECAST
INIT 16/1500Z 19.7N 46.2W 30 KT 35 MPH
12H 17/0000Z 21.3N 47.4W 35 KT 40 MPH
24H 17/1200Z 23.2N 49.0W 45 KT 50 MPH
36H 18/0000Z 24.7N 50.4W 55 KT 65 MPH
48H 18/1200Z 26.2N 52.2W 65 KT 75 MPH
60H 19/0000Z 27.5N 54.1W 75 KT 85 MPH
72H 19/1200Z 28.9N 56.0W 95 KT 110 MPH
96H 20/1200Z 32.8N 58.3W 90 KT 105 MPH
120H 21/1200Z 37.0N 55.2W 80 KT 90 MPH
CIMSS WIND SHEAR AND UPPER LEVEL WINDS


FORECAST CONDITIONS FROM THE ECMWF




I will continue to monitor the progress of TD 15 for any significant changes that may occur to the forecast conditions.

Elsewhere, in about 5 -7 days out in the period, we could see the possibility of something trying to develop either in the GOMEX, or northern Bahamas.  The forecast calls for the MJO to move into a PHASE 3 pattern.  Ridging is forecast to develop over the Great Lakes region, and Canada.  The infamous “ridge over troubled water”.  This pattern has the tendency to to cause height falls south, which usually occur over the GOMEX to the Bahamas.  This is shown in both the ECMWF and GFS, with the GFS actually developing a small system. 
ECMWF AND GFS 500 HEIGHT ANOMALY FORECAST


Should the forecast of the MJO be correct, the following chart indicates observed development of MJO phases, indicated by orange coloring;
MJO OBSERVED DEVELOPMENT PHASES

I’ll be monitoring this over the next week.

The following map will allow to get information from your NWS office.
NWS WATCH / WARNING DISPLAY (LINKED…CLICK MAP, THEN YOUR AREA)

NWS DOPPLER RADAR LOOP (LINKED, CLICK RADAR MAP)

RAP RADAR (CLICK IMAGE THEN RADAR SITE…ONCE YOU CLICK THE SITE, GO TO LOOP DURATION TO CREATE A LOOP)
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Have a blessed day!