237
FXCA20 KWBC 301756
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 PM EDT TUE SEP 30 2025
NOTE: UPDATE ON TROPICAL WAVE CHART.
FORECAST BULLETIN 30 SEPTEMBER 2025 AT 1800 UTC:
ON TUESDAY MORNING, OVER THE BAHAMAS AND THE CARIBBEAN REGION, AN
UPPER RIDGE IS CENTERED OVER THE YUCATAN CHANNEL AND EXTENDS AS A
RIDGE AXIS INTO THE WEST CENTRAL ATLANTIC OCEAN. THIS ANTICYCLONIC
PATTERN IS EXPECTED TO CONTINUE INTO TUESDAY EVENING, WHILE AN
UPPER LEVEL TROUGH OVER THE SOUTHERN UNITED STATES INTERACTS WITH
THE PERIPHERY OF THE UPPER RIDGE AS IT ENTERS OVER FLORIDA BY
WEDNESDAY MORNING. DUE TO THE LOW AMOUNT OF AVAILABLE MOISTURE,
PRECIPITATION MAXIMA OVER NORTH BAHAMAS IS EXPECTED TO RANGE
BETWEEN 20-35MM AS THE TROUGH ASSOCIATED WITH HURRICANE IMELDA
EXTENDS OVER THE REGION ON TUESDAY. THE REST OF THE CARIBBEAN CAN
EXPECT DRY CONDITIONS AS AVAILABLE MOISTURE REMAINS LOW. ON
WEDNESDAY, THE UPPER TROUGH EXTENDS FURTHER SOUTHWARD, WITH A
SHORT WAVE TROUGH EMBEDDED IN THE BASE THAT EXTENDS INTO THE
YUCATAN CHANNEL, WEST CUBA, AND MAKES ITS WAY INTO THE BAHAMAS BY
EARLY THURSDAY MORNING. IN THE LOWER LEVELS, THE TWO TROPICAL
SYSTEMS OVER THE ATLANTIC OCEAN ARE INTERACTING WITH THE FRONTAL
BOUNDARY ASSOCIATED WITH THE WIDER UPPER TROUGH OVER THE EASTERN
SEABOARD OF THE UNITED STATES. THIS WILL ASSIST IN THE DEVELOPMENT
OF A THICKNESS GRADIENT EXTENDING FROM BERMUDA, ASSOCIATED WITH
POST-TROPICAL STORM IMELDA, AND EXTEND WESTWARD OVER THE NORTH
BAHAMAS AND FLORIDA AS A DEVELOPING COLD FRONT. THIS WILL FAVOR
MOISTURE CONVERGENCE ALONG THE FRONTAL BOUNDARY, WITH MAXIMA OF
AROUND 20-35MM IN NORTH BAHAMAS WITH A MARGINAL RISK OF SEVERE
WEATHER DUE TO THE UPPER LEVEL SHORT WAVE TROUGH, AND GENERALIZED
MAXIMA OF 15MM FROM CENTRAL BAHAMAS TO TURKS AND CAICOS. SIMILAR
MAXIMA ARE EXPECTED IN OVER THE GREATER ANTILLES AND THE LEEWARD
ISLANDS WITH THE PRESENCE OF WEAK TROUGHS ALONG THE EASTERLY TRADE
WINDS. BY THURSDAY, THE COLD FRONT PROPAGATES SOUTHWARD INTO THE
CENTRAL ATLANTIC OCEAN, AND BECOMES STATIONARY OVER THE BAHAMAS,
WITH WINDS IN THE LOWER LEVELS BEGIN TO SHIFT FROM THE EAST OVER
NORTHERN BAHAMAS. THIS GIVES WAY TO THE POTENTIAL OF WEAK ECHO
TRAINING ON THURSDAY, AND PRECIPITATION MAXIMA OF 30-60MM. OVER
THE GREATER ANTILLES, THE PRESENCE OF PREFRONTAL TROUGHS OVER THE
REGION WILL FAVOR GENERALIZED MAXIMA OF 15-25MM, AND MAXIMA OF
15MM IN THE LESSER ANTILLES WITH THE PROPAGATION OF TROUGHS IN THE
TRADE WINDS.
IN MEXICO AND CENTRAL AMERICA, AN UPPER LEVEL RIDGE IS PRESENT AND
MEANDERING OVER MEXICO, WHILE CENTRAL AMERICA SEES A GENERAL ZONAL
PATTERN IN THE UPPER LEVELS. THE REGION WILL SEE ACTIVITY FROM THE
PASSAGE OF PROPAGATING TROUGHS OVER THE REGION AND ACTIVITY FROM
THE MONSOON TROUGH MEANDERING JUST SOUTH OF MEXICO AND ENTERING
COSTA RICA ON TUESDAY EVENING, FAVORING MOIST ONSHORE FLOW FROM
CHIAPAS AND ALONG THE PACIFIC COASTS OF CENTRAL AMERICA. THE
AMOUNT OF AVAILABLE MOISTURE OF AROUND 50MM IN PRECIPITABLE WATER
IS EXPECTED TO FLOW INLAND, WHILE INTERACTING WITH THE TERRAIN AND
SEEING OROGRAPHIC LIFT ON TUESDAY. THE GULF OF FONSECA REGION CAN
EXPECT MAXIMA OF 30-60MM AS A MONSOON LOW DEVELOPS WITHIN THE
MONSOON TROUGH, WITH INCREASED ONSHORE FLOW. GENERALIZED MAXIMA OF
20-45MM ARE EXPECTED FROM NAYARIT THROUGH THE SOUTHWESTERN COAST
OF MEXICO, INTO GUATEMALA, AND EXPECTED FROM COSTA RICA INTO
PANAMA ON TUESDAY. ON WEDNESDAY, THE MONSOON TROUGH CONTINUES TO
MEANDER JUST SOUTH OF MEXICO AND CENTRAL AMERICA, ENTERING THROUGH
COSTA RICA. THIS ENHANCED CIRCULATION SHOULD INCREASE MOIST
ONSHORE FLOW, FAVORING MAXIMA OF 25-50MM FROM CHIAPAS TO SOUTHERN
GUATEMALA, AND GENERALIZED MAXIMA OF 20-45MM FROM GUERRERO TO
OAXACA, EL SALVADOR TO NICARAGUA, AND FROM COSTA RICA TO THE
AZUERO PENINSULA IN PANAMA. IN THE GULF OF CAMPECHE, A LOW LEVEL
TROUGH IS PERSISTING AND STRENGTHENING ITS CIRCULATION OVER THE
GULF, INCREASING MOIST ONSHORE FLOW INTO VERACRUZ AND ALONG THE
SIERRA MADRE ORIENTAL. THIS WILL FAVOR MAXIMA OF 25-50MM. TO THE
WEST, FROM NAYARIT TO SOUTH MICHOACAN, ANOTHER LOW LEVEL TROUGH IS
ENHANCED BY MID LEVEL VORTICITY PROPAGATION FROM A MID LEVEL SHORT
WAVE TROUGH, FAVORING MAXIMA OF 20-35MM IN THE REGION. BY
THURSDAY, THE CIRCULATIONS ASSOCIATED WITH THE MONSOON TROUGH
CONTINUE TO INTERACT WITH THE PACIFIC REGIONS OF MEXICO AND
CENTRAL AMERICA. THE AREAS OF HIGHER INTEREST ARE FROM GUERRERO TO
OAXACA, WERE THE EXTENSION OF A TROUGH FROM A MONSOON LOW FAVORS
MAXIMA OF 25-50MM, SIMILARLY SOUTHERN CHIAPAS AND SOUTH GUATEMALA
CAN EXPECT MAXIMA OF 30-60MM. OTHER REGIONS OF SOUTHERN MEXICO,
GUATEMALA, EL SALVADOR AND THE GULF OF FONSECA REGION CAN EXPECT
GENERALIZED MAXIMA OF 20-35MM, IN COSTA RICA AND PANAMA, AN
EASTERLY WAVE IS PROPAGATING INTO THE REGION AND ENHANCING THE
CIRCULATION IN THE MONSOON TROUGH. THIS INTERACTION WILL FAVOR
MAXIMA OF 25-50MM AS OROGRAPHIC LIFT TAKES EFFECT. THERE IS A
POTENTIAL FOR HIGHER AMOUNTS OF PRECIPITATION LOCALLY.
ADDITIONALLY, THE GULF OF CAMPECHE REGION CONTINUES TO SEE THE LOW
LEVEL CIRCULATION OVER THE REGION, WHICH WILL FAVOR MAXIMA OF
35-70MM AS MOISTURE REMAINS IN THE AREA.
IN NORTHERN SOUTH AMERICA, THE PRESENCE OF PROPAGATING LOW LEVEL
TROUGHS ALONG THE TRADE WINDS ENHANCED BY DIURNAL HEATING WILL BE
THE MAIN DRIVER OF PRECIPITATION OVER THE FORECAST PERIOD. ON
TUESDAY, THE PRESENCE OF LONG FETCH, ONSHORE FLOW IN WEST
COLOMBIA, WHERE EXPECT MAXIMA OF 35-70MM. ELSEWHERE IN WEST
COLOMBIA AND INTO ECUADOR AND NORTH PERU, EXPECT MAXIMA OF 20-35MM
WITH THE PRESENCE OF MOISTURE CONVERGENCE ALONG THE ANDES REGIONS.
ON WEDNESDAY, A TROUGH DEVELOPS OVER THE LAKE MARACAIBO REGION,
PROPAGATING WESTWARD OVER NORTHERN COLOMBIA. THIS WILL FAVOR
CYCLONIC CIRCULATION INTO NORTHERN COLOMBIA AND THE LAKE MARACAIBO
REGION, FAVORING MAXIMA OF 20-35MM. TO THE EAST AND SOUTH, THE
PRESENCE OF A TROUGH DEVELOPING OVER VENEZUELA AND THE CENTRAL
AMAZON BASIN DUE TO THE ACTIVATION OF THE SOUTH AMERICAN LLJ
(SALLJ) IN CENTRAL SOUTH AMERICA, WILL FAVOR MAXIMA OF 20-35MM IN
THE REGION, WHILE FROM SOUTH COLOMBIA INTO ECUADOR EXPECT SIMILAR
AMOUNTS. ON THURSDAY, THE TROUGHING OVER THE WEST-CENTRAL AMAZON
BASIN CONTINUES, PROPAGATING WESTWARD, WHERE FROM SOUTH VENEZUELA
TO AMAZONAS-BRASIL AND EASTERN PORTIONS OF ECUADOR AND PERU CAN
EXPECT GENERALIZED MAXIMA OF 20-45MM.
POSITIONS OF TROPICAL/EASTERLY WAVES INITIALIZED AT 12 UTC
TYP SOF INIT 01/00 01/12 02/00 02/12 03/00 03/12 04/00 04/12
TW 11N 44W 45W 47W 49W 51W 52W 53W 54W 55W
TW 15N 52W 54W 56W 57W ABSORBED
EW 11N 67W 70W 73W 75W 77W 79W 81W 82W 83W
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