TROPICAL WEATHER OUTLOOK FORECAST SYNOPSIS…ISSUED AUG. 15, 2023…9:20 P.M. EDT

Disclaimer:  This 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, (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.

The following is my outlook forecast for the 2023 Atlantic Hurricane Season:
STORM W SEASONAL FORECAST
TOTAL NAMED STORMS: 11– 14
TOTAL HURRICANES :        5 – 6
MAJOR HURRICANES:        2 – 3

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

SEASON TOTALS
NAMED STORMS:          4
HURRICANES:                1
MAJOR HURRICANES: 0

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!

The tropics still remain fairly quiet this evening, with a good majority of the basin still being covered in drier air from a combination of the SAL and stable conditions due to sinking air.  However, the 500 mb normalized anomaly pattern has been changing with the ECMWF indicating some reversal in the pattern, with higher anomalies now north of the MDR and lowering anomalies over the MDR.  This has allowed for some increase in vertical instability, however instability is still far below climatology. 
TROPICAL ATLANTIC VERTICAL INSTABILITY

You’ll note that the vertical instability realtime graph is beginning to indicate an increase of vertical instability over the MDR.  Though small, this is somewhat of a good jump, given the angle is almost straight up.  It will remain to be seen however, if this trend continues.  Having analyzed another parameter, the forecast CHI200 forecast anomalies from the ECMWF, GFS, and the CMC global models, as well as the ECMWF EPS and GEFS, all indicate the presence of upward vertical velocity (upward motion) at the 200 mb level in the forecast.  This would indicate divergence aloft, which in turn would create convergence at the ocean surface.  Based on this, the probability for the trend in vertical instability to keep on the increase may be good, although given the flip flop in the pattern over the past month, I am placing this still at low confidence, until I see how the actual forecast pans out over the next 72 – 96 hours.

I have been monitoring the tropical wave near 35W, and the wave near 15W (just getting ready to come of the African coast), which the NHC has included in the 7 day GTWO.
NHC 7 DAY GTWO

The wave near 35W had a very good look to it the other day, however with instability still below climatology, and a little dry air intrusion, convection has waned.  Although the wave to the east seems to have more convection, both areas have a very large circulation associated with them.
WEATHERNERDS GOES 16 IR AND WATER VAPOR LOOP IMAGERY

There are 2 problems with these waves…the large circulations, and the close distance related to each other.  Given these are so close together, they are robbing energy from each other, or competing for energy.  Based on analysis of wind shear and 200 mb streamline forecast maps from the ECMWF, once the second wave exits Africa, both areas are forecast to be beneath a radial shear pattern, and outflow at 200 mb.  By the beginning of next week, per the NHC, the ECMWF indicates conditions to become unfavorable for the wave currently over Africa with an increase in shear, and loss of the favorable 200 mb pattern by the 20th.  The second graphic shows the unfavorable area.
ECMWF SHEAR FORECAST (FAVORABLE)


The current ECMWF EPS cyclone probability forecast indicates the best probability for the wave furthest west to occur during the next 72 hours, and the one over Africa during the next 96 – 120 hours from 12Z.

As these 2 features move along the NHC projected path, both begin to perform a phenomenon that sometime occurs with hurricanes, called the Fujiwara effect.  Although not the true effect, these features begin to merge and start to circle each other, prior to merging into one area of low pressure based on the ECMWF forecast.  This “low” is forecast to have the radial shear pattern overhead until around day 6 – 7.  By 168 hours in the forecast period from 12Z today, the favorable shear pattern begins to turn zonal.  Though the relative humidity forecast indicates ample moisture near the center of both of these features, drier air surrounding them, with the possibility of slight dry air intrusion based on the model forecast, should inhibit significant development, with development being slow to occur.  Currently, the system is forecast to move north of the Lesser Antilles. It appears the ECMWF splits another low from this, and the shear and upper pattern appear very favorable for that particular area which would be located SE of the previous low.  I will continue to watch this for any significant changes that may occur.
ECMWF NORMALIZED MSLP ANOMALY

Elsewhere, both the ECMWF and GFS seem to indicate that a tropical wave comes up from the Caribbean, and enters the GOMEX during the next 7 days.  I know folks have been concerned about this, as the current ECMWF EPS probability indicates a 50% – 60% chance of a tropical depression.  I cannot rule this out at the moment, as the forecast RH at 850 mb is high, but limited and displaced at 500 mb.  A radial shear pattern will be centered over the area, however the outflow pattern will not be optimal over the area, with easterly zonal winds.  Optimal outflow will be located well to the east, based on the ECMWF forecast.  So, as of now, there will be some inhibiting factors.  I will continue to monitor everything in the tropics and modeling for any significant changes to the pattern.
ECMWF EPS CYCLONE FORMATION PROBABILITY
ECMWF RH FORECAST

ECMWF PWAT FORECAST

ECMWF SHEAR PATTERN FORECAST GOMEX

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

Have a blessed evening!

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