GOMEX LOW PRESSURE / TROPICAL STORM SEAN / INVEST 94L AND DEVELOPING NOR’EASTER FORECAST SYNOPSIS…ISSUED OCT. 11, 2023…1:00 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. Unless otherwise noted, satellite imagery is provided through Weathernerds.org

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:          18
HURRICANES:                6
MAJOR HURRICANES:  3

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. Unless we have a system threatening any area, the forecast office will be closed on the weekends.

The area that was INVEST 93L over the GOMEX has been downgraded to a large area of low pressure. This is due to the low being absorbed by a frontal boundary, and now has become frontal and baroclinic in nature.
NHC TAFB SURFACE ANALYSIS (CLICK MAP, THEN CLICK TO ZOOM IN)

GOMEX SATELLITE LOOP IMAGERY

Based on the final track guidance product and forecast steering maps, this system should continue toward the ENE to NE. Last guidance has the “center” crossing over the AL/FL border. Residents along the Gulf coast area may experience gale force winds (39–54 mph) in some areas. The final intensity guidance had forecast wind speeds of between 35 – 45 mph. Some winds could be higher in heavier thunderstorm activity. Small craft should remain in port, and commercial shipping should deviate from the areas to be affected. Some areas may experience some minor coastal flooding. A GALE WARNING is currently in effect for the Gulf coast and coastal waters.
GALE WARNING FROM NWS OFFICE MOBILE
A Gale Warning is in effect from 11 AM today through 6 AM Thursday for the offshore Gulf Waters and all area bays and sounds for east winds 20 to 30 knots with gusts of 35 to 45 knots and seas 7 to 10 feet. Strong winds can cause hazardous seas which could capsize or damage vessels and reduce visibility. Mariners should consider altering plans to avoid these potential hazardous conditions. Remain in port, seek safe harbor, alter course, or secure vessels for high winds and seas.
The following are animations from both the ECMWF and GFS:

5 DAY TOTAL PRECIPITATION FORECAST

WAVEWATCH 3 SIGNIFICANT WAVE HEIGHT FORECAST

This will be my last update on this system. Please refer to the NWS HAZARDS AND WARNINGS map at the bottom of the page for information from your local NWS office regarding this system.

Elsewhere, NHC is at it again. We now have Tropical Storm SEAN.

Based on my analysis of visible satellite loop imagery, the LLC has become exposed, and there appears to be a multiple vortex situation, and some slight dry air entrainment, creating a disorganized system.
SEAN SATELLITE LOOP IMAGERY

As of the 11:00 a.m. EDT advisory from the NHC, the following was available on Tropical Storm? SEAN:
11:00 AM AST Wed Oct 11
Location: 10.9°N 34.4°W
Moving: WNW at 13 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 40 mph
SEAN is currently under moderate wind shear. Based on analysis of forecast shear maps wind shear should subside somewhat in about 18 hours. This may allow for a breif period of slight strengthening. However, based on analysis of the mid level moisture forecast and SHIPS diagnostic report, mid level moisture should become less favorable after the 48 hour period in the forecast, dropping below 60% relative humidity. This should begin to weaken SEAN. Based on these factors, I currently agree with the NHC intensity forecast.
NHC INTENSITY FORECAST

INIT  11/1500Z 10.9N  34.4W   35 KT  40 MPH
 12H  12/0000Z 11.2N  35.8W   35 KT  40 MPH
 24H  12/1200Z 11.7N  37.4W   40 KT  45 MPH
 36H  13/0000Z 12.4N  38.9W   40 KT  45 MPH
 48H  13/1200Z 13.1N  40.5W   40 KT  45 MPH
 60H  14/0000Z 14.1N  41.9W   40 KT  45 MPH
 72H  14/1200Z 15.1N  43.0W   35 KT  40 MPH
 96H  15/1200Z 16.8N  45.3W   35 KT  40 MPH
120H  16/1200Z 18.1N  48.9W   30 KT  35 MPH...POST-TROP/REMNT LOW

CIMSS WIND SHEAR MAP

SEAN is moving toward the WNW at the moment. I expect this motion to continue during the next 36 – 48 hours. Thereafter there has been a change to the forecast guidance. Based on my analysis of forecast steering and MSLP anomaly animations, ridging is supposed to build back in to the north of the system, with the storm making a more left bend, with the track becoming WNW. If you recall, initially and for about 4 days, models and guidance had this re-curving. Based on the analysis and new information, I agree with the current guidance and NHC forecast track.
12Z GUIDANCE

NHC FORECAST TRACK
cone graphic
I will continue to monitor this system during the remainder of the week, and will update if necessary.

Elsewhere, we now have INVEST 94L from a tropical wave that has exited the African coast. As of the 12Z ATCF BTK product, the following was available on INVEST 94L:
8:00 AM AST Wed Oct 11
Location: 10.9°N 34.4°W
Moving: W at 8 mph
Min pressure: 10011 mb / 29.85 in
Max sustained: 35 mph
Based on analysis of forecast steering, 500 mb anomaly and geopotential height forecasts, I expect a general westward motion to continue over the next 96 hours. I am going to monitor this closely, as based on the NHC 7 day graphical tropical weather outlook (GTWO) forecast, and the items I just mentioned, this could be a straight runner, and could possibly affect the Windward / Leeward islands, as current modeling indicates ridging to remain north of the system. The ECMWF seems to indicate a weak system in that vicinity at 10 days out. Even though the items analyzed indicate this possibility, initial guidance and forecast maps beyond 7 to 10 days do lose accuracy. Since this system was just initialized and data fed into the computers is sparse at the moment, consider forecast track guidance low confidence at the moment. A good example is the track change in SEAN.
NHC 7 DAY GTWO

ECMWF 9 DAY MSLP ANOMALY FORECAST

Satellite loop imagery seems to indicate 94L is slowly trying getting its act together, and is getting “that look” I detected a little bit of dry air intrusion based on the presence of arc clouds to the west.
INVEST 94L SATELLITE LOOP IMAGERY

Analysis of forecast wind shear, moisture and CHI200 maps indicate conditions slowly improving to a more favorable environment over the next 96 – 120 hours with fluctuating conditions thereafter. The CHI200 forecast for the most part indicates a divergent upper pattern to remain in place. Current shear and upper level wind maps from CIMSS indicate a radial shear pattern could be developing as well as an outflow pattern.
CIMSS WIND SHEAR AND UPPER LEVEL WINDS

Intensity guidance was very limited, however given the current forecast conditions, INVEST 94 L may become a tropical depression within the next 36 – 48 hours. I will continue to monitor this system closely, and will update as necessary.

Finally, a Nor’easter is forecast to develop off the mid Atlantic coast by the weekend, becoming a Miller “type B” storm. Click on the graphic for the explanation of both the type B and type A.

A low is forecast to traverse the Great Lakes and Ohio Valley region, and move off the mid Atlantic coast. As this low hits the warm Gulfstream waters, it will begin to deepen and continue to do so, as it eventually moves off toward the NE. The worse effects from this system should be offshore over the Atlantic. Commercial shipping should take evasive action as this moves offshore. Please refer to the NWS HAZARDS and WARNINGS map for any local statements and warnings.
ECMWF MSLP ANOMALY, SURFACE WINDS AND PRECIPITATION FORECAST:

WAVEWATCH 3 FORECAST

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)
CARIBBEAN RADAR (CLICK IMAGE)

You may direct any questions by contacting me personally, ANYTIME, at: twalsh22000@yahoo.com