254
FXCA20 KWBC 191817
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
217 PM EDT FRI SEP 19 2025
FORECAST BULLETIN 19 SEPTEMBER 2025 AT 1820 UTC:
OVER THE WEEKEND, THE PRESENCE OF AN ATMOSPHERIC KELVIN WAVE WILL
FAVOR THE ENHANCEMENT OF PRECIPITATION IN THE REGION AS IT
PROPAGATES OVER THE FORECAST REGION. THE UPPER LEVEL DIVERGENCE
ASSOCIATED WITH IT WILL LINGER INTO EARLY MONDAY, ALTHOUGH MUCH OF
THE EFFECTS ARE ANTICIPATED OVER THE CENTRAL ATLANTIC OCEAN AND
PORTIONS OF THE EAST CARIBBEAN SEA REGION.
OF INTEREST IS THE PRESENCE OF A DEEP MID TO UPPER LEVEL TROUGH
THAT EXTENDS FROM THE SOUTHERN UNITED STATES INTO THE YUCATAN
PENINSULA AND PORTIONS OF THE NORTHWEST CARIBBEAN ON FRIDAY
MORNING. ALONG THE BASE AND PERIPHERY OF THE TROUGH, SHORTWAVE
TROUGHS ARE EXPECTED TO PROPAGATE INTO THE YUCATAN PENINSULA AND
CUBA FROM FRIDAY INTO SATURDAY MORNING. THESE CONDITIONS ARE
EXPECTED TO CONTINUE, AS THAT UPPER LEVEL TROUGH MEANDERS THE SAME
REGION INTO NEXT WEEK. A PERSISTENT TROUGH REFLECTED IN THE LOWER
LEVELS ALONG THE UNITED STATES EASTERN SEABOARD EXTENDS INTO NORTH
BAHAMAS AND MEANDERS OVER THE REGION ON FRIDAY, WHERE AVAILABLE
MOISTURE RANGING AROUND 45-55MM AND PRECIPITATION MAXIMA OF
15-30MM ARE EXPECTED, IN ADDITION TO A MARGINAL RISK OF SEVERE
WEATHER. OTHER LOW LEVEL TROUGHS DEVELOP OVER CUBA DUE TO THE
UPPER LEVEL TROUGH, WHILE PROPAGATING TROUGHS IN THE EASTERLY
TRADE WINDS ENTER THE REGION OF THE CARIBBEAN OVER THE WEEKEND.
FRIDAY IS EXPECTED TO BE THE DAY WITH HIGHER AMOUNTS OF AVAILABLE
MOISTURE, AND BY SATURDAY AND SUNDAY, DRIER AIR IS ADVECTED FROM
THE EAST. ON SATURDAY AND SUNDAY, CONTINUED TROUGHING IS EXPECTED
TO PERSIST IN THE BAHAMAS REGION, AND PRECIPITATION VALUES BELOW
25MM ARE EXPECTED BOTH DAYS.
TO THE WEST, AN UPPER LEVEL RIDGE EXTENDS FROM THE EAST PACIFIC
OCEAN AND INTO CENTRAL AND SOUTHERN REGIONS OF MEXICO ON FRIDAY.
AS THE SUBTROPICAL JET STREAM STRENGTHENS OVER THE CENTRAL UNITED
STATES, THE UPPER RIDGE MEANDERS INTO CENTRAL MEXICO AND
STRENGTHENS OVER THE REGION BY SUNDAY. WHILE INTERACTING WITH THE
UPPER TROUGH IN THE EAST, THE PROPAGATION OF SHORTWAVE TROUGHS IN
THE MID LEVELS ALONG SOUTHERN MEXICO AND NORTH CENTRAL AMERICA
WILL ASSIST WITH DEEPER CONVECTION OVER THE WEEKEND. ADDITIONALLY,
A TROPICAL WAVE PROPAGATES FROM THE GULF OF TEHUANTEPEC REGION ON
FRIDAY TO SOUTHWEST MEXICO BY MONDAY MORNING. AS THIS WAVE
CONTINUES MOVING ALONG THE MONSOON TROUGH, IT EXPERIENCES ENHANCED
CIRCULATION JUST SOUTH OF THE COASTAL REGIONS IN SOUTHWEST MEXICO,
FAVORING MOIST ONSHORE FLOW ALONG THE COAST. EXPECT PRECIPITATION
MAXIMA TO RANGE FROM 30-60MM FROM COASTAL SOUTH GUATEMALA THROUGH
SOUTHWEST MEXICO ON FRIDAY, FROM OAXACA TO GUERRERO ON SATURDAY
AND SUNDAY, AS THIS WAVE MOVES WESTWARD. THE BASE OF THE UPPER
TROUGH EXTENDS INTO NORTHERN CENTRAL AMERICA, WHERE THEY CAN
EXPECT TO SEE MOISTURE ENTER THE REGION WITH THE PASSING OF
TROUGHS ENHANCED BY THE UPPER LEVEL CONDITIONS. FROM THE YUCATAN
PENINSULA THROUGH THE GULF OF FONSECA REGION, EXPECT PRECIPITATION
MAXIMA OF 20-35MM ON FRIDAY. THE YUCATAN CAN EXPECT A DECREASE IN
PRECIPITATION ON SATURDAY, WITH THE DECREASE IN AVAILABLE
MOISTURE, WHILE HONDURAS AND THE GULF OF FONSECA REGION CAN SEE
SIMILAR AMOUNTS AS FRIDAY. BY SUNDAY, THE REGION CAN EXPECT A
GENERALIZED DECREASE IN AVAILABLE MOISTURE, WITH THE EXCEPTION OF
CENTRAL GUATEMALA AND INTO TABASCO AND CHIAPAS, WHERE EXPECT
RAINFALL MAXIMA RANGING FROM 20-45MM.
FROM NICARAGUA TO NORTH SOUTH AMERICA, THE PASSING OF TROUGHS IN
THE TRADE WINDS IN THE WESTERN PORTION WILL BE A DRIVING FACTOR
FOR PRECIPITATION OVER THE FORECAST PERIOD. TO THE EAST, A DRYING
TREND IS EXPECTED AS MOISTURE DECREASES WITH DRY AIR ADVECTION
FROM THE EASTERLY TRADE WINDS. IN THE UPPER LEVELS, AN UPPER
TROUGH PROPAGATES OVER NORTH VENEZUELA AND NORTH COLOMBIA ON
FRIDAY INTO THE WESTERN CARIBBEAN, AND SOUTH CENTRAL AMERICA BY
LATE SATURDAY. THIS UPPER TROUGH WILL BE REPLACED BY THE PERIPHERY
OF A STRENGTHENING UPPER RIDGE CENTERED BY CENTRAL BOLIVIA AND
BRASIL, AND A WEAK JET IN THE UPPER LEVELS COULD ASSIST WITH
ENHANCED UPPER LEVEL SPEED DIVERGENCE ON SUNDAY. IN THE LOWER
LEVELS, A MOIST TROUGH IS PROPAGATING NORTH AND WESTWARD, OVER
WEST VENEZUELA AND INTO COLOMBIA BY FRIDAY EVENING. THE MOISTURE
CONVERGENCE EXPECTED ALONG THE ANDEAN REGION OF COLOMBIA AND THE
LAKE MARACAIBO REGION OF VENEZUELA WILL FAVOR PRECIPITATION MAXIMA
RANGING 20-45MM, WITH LOCALLY HIGHER AMOUNTS OF PRECIPITATION.
MOIST ONSHORE FLOW IN WEST COLOMBIA CAN FAVOR SIMILAR AMOUNTS ON
FRIDAY, AND SIMILAR AMOUNTS ARE EXPECTED ON SATURDAY AS THE TROUGH
CONTINUES TO PROPAGATE OVER CENTRAL COLOMBIA. BY SUNDAY EVENING,
THE TROUGH IS EXPECTED OVER THE DARIEN REGION OF PANAMA, FAVORING
WESTERLY AND MOIST ONSHORE FLOW IN FROM THE DARIEN REGION AND
ALONG WEST COLOMBIA. AS SUCH THE REGION CAN EXPECT RAINFALL MAXIMA
OF 30-60MM, WITH THE ASSISTANCE OF SPEED DIVERGENCE IN THE UPPER
LEVELS. THE PRESENCE OF THE MONSOON TROUGH WILL FAVOR MODERATE
PRECIPITATION IN NORTH COLOMBIA AND NORTH VENEZUELA ON SUNDAY.\
POSITIONS OF TROPICAL/EASTERLY WAVES INITIALIZED AT 12 UTC
TYPE SOF INIT 20/00 20/12 21/00 21/12 22/00 22/12 23/00 23/12
TW 16N 35W 38W 41W 45W 48W 51W 54W 57W 60W
TW 19N 95W 96W 97W 99W 101W 103W 105W 106W 107W
TW 22N 113W 114W 115W 116W 117W EXITS
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