239
FXCA20 KWBC 171804
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 PM EDT WED SEP 17 2025
FORECAST BULLETIN 17 SEPTEMBER 2025 AT 1800 UTC:
SYNOPSIS:
THE PRESENCE OF AN ATMOSPHERIC KELVIN WAVE IS EXPECTED OVER THE
FORECAST REGION, WHICH WILL AID IN PROVIDING UPPER-LEVEL
DIVERGENCE AND ENHANCE CONVECTION OVER THE NEXT SEVERAL DAYS. A
NEARLY STATIONARY DEEP TROUGH IN THE MID-LATITUDES WILL CONTINUE
REMAIN IN PLACE FOR MUCH OF THE REGION FOR THE NEXT FEW DAYS.
THESE FACTORS, ALONG WITH MOISTURE DUE TO THE PRESENCE OF THE
MONSOON TROUGH, AND A WESTWARD MOVING TROPICAL WAVE WILL CONTINUE
TO INFLUENCE PRECIPITATION TOTALS IN MEXICO AND CENTRAL AMERICA.
IN THE BAHAMAS AND THE GREATER ANTILLES, THE INTERACTION OF THE
TROUGH WILL BRING DAILY PRECIPITATION AND POSSIBLE SEVERE WEATHER
TO CUBA AND THE BAHAMAS, WITH A SLIGHT RISK OF SEVERE WEATHER
POSSIBLE IN CUBA ON THURSDAY. MEANWHILE, THE ENTRANCE OF A
TROPICAL WAVE WILL BRING PRECIPITATION TO HISPANIOLA AND PUERTO
RICO ON FRIDAY, POTENTIALLY BRINGING SEVERE WEATHER WITH IT. IN
SOUTH AMERICA, LOW-LEVEL MOISTURE ENTERING INTO THE WEST COAST OF
COLOMBIA WILL BRING HIGH PRECIPITATION TO THE NORTHWEST OF SOUTH
AMERICA, WHILE IN NORTH-CENTRAL SOUTH AMERICA, MOST PRECIPITATION
WILL BE CAUSED BY LOCALLY INDUCED CONVECTION.
MEXICO AND CENTRAL AMERICA:
MOST PRECIPITATION OVER THE NEXT FEW DAYS WILL CONTINUE DUE TO A
DEEP TROUGH IN THE MID-LATITUDES EXTENDING FROM THE SOUTHERN
UNITED STATES AND WITH A BASE IN THE YUCATAN PENINSULA, WITH
PRECIPITATION EXPECTED FOR MUCH OF SOUTHEAST MEXICO AND GUATEMALA.
IN THE LOWER LEVELS THERE IS AN INDUCED TROUGH EXTENDING OVER THE
BAY OF CAMPECHE INTO THE YUCATAN PENINSULA/GUATEMALA REGION, WITH
A PERSISTENT INFLUX OF MOISTURE ALONG WITH LOW-LEVEL CONVERGENCE,
PARTICULARLY TODAY INTO THURSDAY. THIS WILL RESULT IN HEAVY AND
LOCALIZED PRECIPITATION FOR THIS REGION BUT ALSO INCLUDING EL
SALVADOR AND THE GULF OF FONSECA TODAY AND THURSDAY, WITH UP TO
30-60MM EXPECTED TODAY.
IN NORTHWEST MEXICO, UPPER-LEVEL DIVERGENCE FROM THE EASTERN
PERIPHERY OF THE SEASONAL UPPER-LEVEL RIDGE, ALONG WITH MID-LEVEL
SUPPORT BY WAY OF A SUBTLE INVERTED TROUGH AND LOW-LEVEL MOISTURE
CONVERGENCE, WILL RESULT IN DAILY DEEP CONVECTION THROUGHOUT MUCH
OF WEST MEXICO FOR THE NEXT FEW DAYS. HIGHEST PRECIPITATION
AMOUNTS WILL OCCUR OVER SOUTHERN SONORA, ALL OF SINALOA, AND THE
WESTERN PORTIONS OF CHIHUAHUA AND DURANGO, AND SHOULD PEAK AT
ABOUT 20-45MM DAILY.
IN COSTA RICA AND PANAMA, THE MONSOON TROUGH WILL CONTINUE TO
REMAIN IN PLACE JUST NORTH OF COSTA RICA, WITH THE ADDITIONAL
ENTRANCE OF A TROPICAL WAVE, CURRENTLY LOCATED AROUND 81W,
BRINGING IN ADDITIONAL PRECIPITATION.A LOW-LEVEL CIRCULATION WILL
FAVOR MOIST ONSHORE FLOW FROM THE PACIFIC OCEAN INTO THE
GUANACASTE AND TO THE AZUERO PENINSULA, WHILE TO THE EAST, ONSHORE
FLOW IS EXPECTED FROM ALONG EASTERN COSTA RICA INTO BOCAS DEL TORO
REGION IN PANAMA FROM THE CARIBBEAN SEA. THIS WILL RESULT IN HEAVY
PRECIPITATION, UPWARDS OF 25-50MM, ON THURSDAY TO THIS REGION.
THE BAHAMAS AND CARIBBEAN:
MUCH OF THE SETUP WILL REMAIN THE SAME FOR THE REST OF THE WEEK AS
IN PREVIOUS DISCUSSIONS. THE VERTICALLY STACKED TROUGH WILL
CONTINUE ITS SLOW EASTWARD PROGRESSION, CONTINUING TO AFFECT
NORTHERN CUBA AND THE BAHAMAS. THE TROUGHâ€S POSITION WILL RESULT
IN VERY STRONG UPPER-LEVEL DIVERGENCE AND LOW-LEVEL INSTABILITY,
WITH DAILY CONVECTION LIKELY FOR THE NEXT THREE DAYS. THIS COULD
BRING SEVERE WEATHER TO BOTH CUBA AND THE BAHAMAS, WITH A SLIGHT
RISK OF SEVERE WEATHER POSSIBLE IN CUBA, AND MARGINAL RISK OF
SEVERE WEATHER IN THE BAHAMAS TODAY. THERE IS ALSO AN ELEVATED
RISK OF HAIL ANTICIPATED FOR CUBA TODAY. ON THURSDAY, THE MARGINAL
RISK WILL CONTINUE IN THE BAHAMAS, AND A MAXIMUM OF 20-45MM OF
PRECIPITATION IS EXPECTED THAT DAY.
IN HISPANIOLA AND PUERTO RICO, A TROPICAL WAVE, LOCATED AROUND
65W, IS EXPECTED TO CONTINUE ITS WESTWARD PROPAGATION THROUGH
PUERTO RICO TODAY, APPROACHING HISPANIOLA TOMORROW, FAVORING
PRECIPITATION. THE INTERACTION OF THE TROPICAL WAVE WITH
HISPANIOLAâ€S TOPOGRAPHY WILL RESULT IN HEAVY LOCALIZED
PRECIPITATION ON THURSDAY INTO FRIDAY, BRINGING A MAXIMUM OF
25-50MM IN SOME AREAS. THE REMNANTS OF THE TROPICAL WAVE IS ALSO
EXPECTED TO AFFECT THE LEEWARD ISLANDS TODAY WITH A MARGINAL RISK
OF SEVERE WEATHER. PRECIPITATION TOTALS ARE EXPECTED TO PEAK AT
20-35MM FOR THE LEEWARD ISLANDS TODAY.
TROPICAL SOUTH AMERICA:
IN NORTHWEST SOUTH AMERICA, ENHANCED UPPER-LEVEL DIVERGENCE OFF
THE WESTERN COAST AND THE HIGH INFLUX OF MOISTURE IN THE LOWER
LEVELS VIA THE CIRCULATION OF THE PANAMANIAN LOW WILL BRING HIGH
AMOUNTS OF PRECIPITATION, ESPECIALLY ON THE WEST COAST OF
COLOMBIA. PRECIPITATION SHOULD BE ITS HIGHEST TODAY, PEAKING AT
AROUND 25-50MM. PRECIPITATION AMOUNTS SHOULD THEN BEGIN TO
DECREASE SLIGHTLY ON THURSDAY AND FRIDAY, AT AROUND 20-45MM. IN
NORTH-CENTRAL SOUTH AMERICA, THE PRESENCE OF A SMALL AND SUBTLE
UPPER-LEVEL TROUGH LOCATED IN NORTHEAST COLOMBIA WILL BE OF
INTEREST, AND SHOULD AID IN SLIGHT ENHANCEMENT OF UPPER-LEVEL
DIVERGENCE ON THE EASTERN SIDE OF THE TROUGH. THIS WILL ENHANCE
AND DEEPEN THE LOCAL CONVECTION EXPECTED, PARTICULARLY ON THURSDAY
IN THE NORTH-CENTRAL REGION OF SOUTH AMERICA, AND WILL BRING
PRECIPITATION OF UP TO 20-35MM WITH LOCALLY HIGHER AMOUNTS
POSSIBLE.
POSITIONS OF TROPICAL/EASTERLY WAVES INITIALIZED AT 12 UTC
TYPE SOF INIT 18/00 18/12 19/00 19/12 20/00 20/12 21/00
21/12
TW 25N 45W 47W 49W 51W 53W 55W 57W 59W
61W
TW 25N 65W 68W 71W 73W 75W 76W
ABSORBED----------
TW 19N 81W 83W 86W 89W 92W 94W 96W 98W
100W
TW 17N 106W 107W 109W 111W 113W 115W 117W
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