TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
141 PM EDT TUE SEP 17 2024

FORECAST BULLETIN 17 SEP 2024 AT 1740 UTC:

A QUASI-STATIONARY UPPER FLOW PATTERN HAS ESTABLISHED ACROSS
MEXICO AND THE SOUTHEAST USA/FLORIDA. THIS IS CHARACTERIZED BY AN
UPPER RIDGE FORECAST TO CENTER OVER THE SOUTHERN GULF OF
CALIFORNIA/CENTRAL MEXICO THROUGH EARLY FRIDAY...AND AN UPPER
TROUGH FORECAST TO EXTEND ACROSS THE SOUTHEAST USA INTO THE
YUCATAN PENINSULA. THE RUDGE IS FORECAST TO VENTILATE CONVECTION
ACROSS MOST SOUTHERN AND SOUTHEAST MEXICO WHERE ENHANCED VALUES OF
AVAILABLE MOISTURE ARE PRESENT. YET...ELSEWHERE IN MEXICO EXPECT
GENERALLY DRY CONDITIONS AND VERY CONSERVATIVE PRECIPITATION
AMOUNTS FOR THIS TIME OF THE YEAR. IN SOUTHERN MEXICO...MOST OF
THE ACTIVITY WILL ORGANIZE WITH TROPICAL WAVES (SEE BELOW FOR
POSITIONS AND IMPACTS).

THE AFOREMENTIONED QUASI-STATIONARY UPPER TROUGH IN THE SOUTHEAST
USA/FLORIDA WILL FAVOR SEVERAL DAYS WITH PRECIPITATION IN CUBA AND
THE BAHAMAS. MID-UPPER COLD AIR AND VENTILATION ASSOCIATED WITH
THE TROUGH WILL FAVOR A WINDOW FOR SEVERE CONVECTION ON TUESDAY.
THROUGH EARLY WEDNESDAY EXPECT MAXIMA OF 25-50MM AND A SLIGHT RISK
FOR SEVERITY IN THE NORTHWEST BAHAMAS. IN NORTH AND WEST CUBA
EXPECT MAXIMA OF 25-50MM. ON WEDNESDAY EXPECT 10-15MM/DAY AND
MAXIMA OF 20-45MM IN CENTRAL AND WEST CUBA AND IN THE NORTHWEST
BAHAMAS. THIS DECREASES TO MAXIMA OF 20-35MM ON THURSDAY.

QUIET CONDITIONS ARE EXPECTED TO CONTINUE IN THE NORTHEAST
CARIBBEAN AS A DRY AIR MASS CONTINUES PROPAGATING WESTWARD. MOST
OF THE ACTIVITY WILL CLUSTER IN THE WINDWARD ISLANDS...DUE TO THE
INFLUENCE OF A CONVERGENCE ZONE ORIGINALLY ASSOCIATED WITH THE
ITCZ/MONSOON TROUGH AND TROPICAL DEPRESSION GORDON...NOW
DISSIPATED. AS THIS CONVERGENCE ZONE WEAKENS...EXPECT CONTINUED
MODERATE RAINFALL ACCUMULATION. THROUGH EARLY WEDNESDAY EXPECT
MAXIMA OF 15-30MM IN THE WINDWARD ISLANDS. THIS DECREASES TO
MAXIMA OF 15-20MM ON WEDNESDAY. BY THURSDAY...AS A BROAD LOW-LEVEL
TROUGH ORGANIZES TO THE NORTHEAST OF THE LESSER ANTILLES...EXPECT
THE AREA OF ENHANCED CONVERGENCE TO MEANDER NORTHWARD INTO THE
CENTRAL LESSER ANTILLES TO FAVOR MAXIMA OF 15MM.

CENTRAL AMERICA IS A REGION OF INTEREST LATE IN THE FORECAST CYCLE
AND INTO THE WEEKEND DUE TO INCREASING POTENTIAO FOR THE FORMATION
OF A CENTRAL AMERICAN GYRE (CAG). THE FACTORS IN PLAY INCLUDE THE
MID-UPPER TROUGH DEEPENING ACROSS THE SOUTHEAST USA INTO NORTHERN
CENTRAL AMERICA THROUGH THE WEEKEND...THE PILING UP OF MOISTURE
ASSOCIATED WITH SLOWING WAVES IN THE TRADES...AND INCREASINGLY
FAVORABLE MJO CONDITIONS INCLUDING THE ARRIVAL OF A TROPOSPHERIC
KELVIN. THERE IS LIMITED CONFIDENCE ON THE AREAS OF THE HEAVIEST
PRECIPITATION AND THE PRECISE TIMING. BUT THE PERIOD OF INTEREST
STRETCHES FROM FRIDAY INTO MID NEXT WEEK. IN THE MEAN
TIME...EXPECT A GRADUAL INCREASE IN AREAS OF DIURNAL CONVECTION AS
WELL AS IN ASSOCIATED RAINFALL ACCUMULATIONS...PARTIALLY FAVORED
BY WAVES PROPAGATED IN THE TRADES (SEE BELOW).

EASTERLY/TROPICAL WAVES INITIALIZED AT 12 UTC
TYPE INIT SOF 18/00 18/12 19/00 19/12 20/00 20/12 21/00 21/12
EW    71W 16N   74W   77W   80W   82W   84W   85W   86W  CAG
TW    82W 17N   84W   86W   89W   92W   93W   95W   98W  100W

AN EASTERLY WAVE IS ORGANIZING NEAR 71W ON WEDNESDAY MORNING. THIS
WAVE IS FORECAST TO AMPLIFY ACROSS THE WESTERN CARIBBEAN TO ARRIVE
IN THE CARIBBEAN COASTS OF NICARAGUA AND COSTA RICA DURING THE DAY
ON THURSDAY. IT IS THEN FORECAST TO SLOW DOWN AND DISSIPATE
POTENTIALLY YILENDING TO THE FORMATION OF A CENTRAL AMERICAN GYRE
(CAG) ON FRIDAY. THE WAVE WILL FAVOR MAXIMA OF 20-35MM IN MOST OF
PANAMA ON WEDNESDAY. ON THUSDAY IT WILL FAVOR MAXIMA OF 30-60MM IN
WEST PANAMA AND MOST OF COSTA RICA...AS WELL AS IN NICARAGUA AND
EAST HONDURAS.

AN ILL-DEFINED TROPICAL WAVE IS PROPAGATING ACROSS CENTRAL AMERICA
ON TUESDAY. THROUGH EARLY WEDNESDAY IT WILL FAVOR MAXIMA OF
20-40MM/DAY IN MOST OF NICARAGUA...COSTA RICA AND WESTERN PANAMA.
ON WEDNESDAY IT WILL FAVOR MAXIMA OF 20-45MM FROM THE GULF OF
FONSECA/SOUTHERN HONDURAS INTO MOST OF GUATEMALA AND CHIAPAS. ON
THURSDAY IT WILL FAVOR MAXIMA OF 20-35MM IN OAXACA AND GUERRERO.

TINOCO...(WPC)
GALVEZ...(WPC)