578
FXCA20 KWBC 221815
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 PM EDT MON SEP 22 2025
FORECAST BULLETIN 22 SEPTEMBER 2025 AT 1815 UTC:
SYNOPSIS:
THE PASSAGE OF TROPICAL STORM NARDA SOUTH OF MEXICO, AND THE
ENTRANCE OF A TROPICAL WAVE THROUGH THE CARIBBEAN WILL BE THE
BIGGEST CONCERNS THROUGHOUT THE WEEK. LOCALLY HEAVY RAINFALL IS
EXPECTED IN SOUTHERN MEXICO AS TROPICAL STORM NARDA TRAVERSES
THROUGH THE COAST FOR THE REST OF TODAY. AN UPPER- AND MID-LEVEL
TROUGH WILL REMAIN IN PLACE IN THE CENTRAL GULF, THE YUCATAN
PENINSULA, AND GUATEMALA, BRINGING HEAVY RAINFALL EARLY THIS WEEK
TO THIS AREA. THIS TROUGH WILL ALSO BRING PRECIPITATION INTO CUBA
AND THE BAHAMAS TODAY INTO TOMORROW. THE PANAMANIAN LOW WILL
CONTINUE TO PROVIDE SIGNIFICANT MOISTURE TO COSTA RICA EARLY THIS
WEEK, WITH LOCALLY HIGH RAINFALL TOTALS EXPECTED, BEFORE BECOMING
LIGHTER MID-WEEK. IN TROPICAL SOUTH AMERICA, DAILY LOCAL
CONVECTION WILL CONTINUE ON TUESDAY AFTER THE DEPARTURE OF DRY AIR
TONIGHT.
MEXICO AND CENTRAL AMERICA:
HEAVY RAINFALL AND LOCALLY HIGH PRECIPITATION TOTALS ARE EXPECTED
ON THE SOUTHERN COAST OF MEXICO AS TROPICAL STORM NARDA SKIRTS THE
COAST. NARDA IS EXPECTED TO CONTINUE IMPACTING THE REGION INTO
TONIGHT, BEFORE MOVING OUT TO SEA STARTING ON TUESDAY. TOTAL
PRECIPITATION OF UP TO 50-100MM IS EXPECTED ON THE FAR SOUTHERN
COASTS OF MEXICO, INCLUDING GUERRERO, JALISCO, MICHOACAN, NAYARIT,
AND COLIMA. REMNANT MOISTURE ASSOCIATED WITH THE SYSTEM HOWEVER
WILL REMAIN THROUGH THE DAY WEDNESDAY, WITH LOCAL AND
OROGRAPHICALLY INDUCED CONVECTION EXPECTED AFTERWARDS.
IN THE YUCATAN PENINSULA AND GUATEMALA, THE INFLUENCE OF AN UPPER-
AND MID-LEVEL TROUGH WILL CONTINUE TO BRING RAINFALL EARLY THIS
WEEK. THE INTERACTION OF THE UPPER TROUGH ALONG WITH STRONG FLOW
FROM THE SOUTHEAST PERIPHERY OF THE RIDGE IN NORTH-CENTRAL MEXICO
WILL BE CONDUCIVE TO STRONG UPPER-LEVEL DIVERGENCE IN THE YUCATAN
PENINSULA REGION. MEANWHILE, IN THE LOWER-LEVELS, A STRONG INFLUX
OF MOISTURE WILL PROMOTE HEAVY PRECIPITATION IN THE REGION TODAY
THROUGH WEDNESDAY.
IN COSTA RICA, THE INFLUENCE OF THE PANAMANIAN LOW WILL CONTINUE
TO BRING ONSHORE FLOW FROM THE ATLANTIC TODAY AND TONIGHT,
BRINGING HEAVY PRECIPITATION WITH LOCALLY HIGH PRECIPITATION
TOTALS POSSIBLE DUE TO OROGRAPHIC EFFECTS. PRECIPITATION ON
TUESDAY AND WEDNESDAY FOR THIS REGION WILL BE LIGHTER, WITH
LOCALLY HIGH AMOUNTS STILL POSSIBLE.
THE BAHAMAS AND THE CARIBBEAN:
THE PRESENCE OF THE PREVIOUSLY MENTIONED DEEP UPPER-LEVEL TROUGH
WILL CONTINUE TO EXTEND INTO THE YUCATAN PENINSULA FROM THE
SOUTHERN UNITED STATES, IN WHICH THE DIVERGENT SIDE OF THE TROUGH
WILL REMAIN SITUATED OVER CUBA AND THE BAHAMAS TODAY. THIS WILL
ALLOW FOR STRONG UPPER-LEVEL DIVERGENCE, AND DIFFLUENCE TO OCCUR
ALOFT, WHICH WILL BE CONDUCIVE FOR CONVECTION. IN THE LOWER
LEVELS, THERE WILL BE SUFFICIENT MOISTURE ADVECTED INTO THE
REGION, WITH PWAT VALUES APPROACHING 60MM. GIVEN THIS SETUP,
CONVECTIVE SUPPORT FROM OROGRAPHIC LIFT, AND MODERATELY STEEP
LAPSE RATES, HEAVY PRECIPITATION IS EXPECTED TODAY IN CUBA AND THE
BAHAMAS WITH A SLIGHT RISK OF SEVERE WEATHER IN NORTHWEST CUBA
INTO TUESDAY.
IN THE GREATER AND LESSER ANTILLES, A TROPICAL WAVE IS FORECAST TO
MAKE ITS WAY THROUGH THE REGION BEGINNING ON TUESDAY, WITH HEAVY
PRECIPITATION EXPECTED THROUGH THE MIDDLE OF THE WEEK. THIS WILL
BRING RAINFALL OF UP TO 30-60MM TO THE LEEWARD ISLANDS BEGINNING
EARLY TUESDAY MORNING, BEFORE MAKING ITS WAY TO PUERTO RICO, WITH
TOTALS ALSO REACHING 30-60MM TUESDAY EVENING AND WEDNESDAY. ON
FRIDAY, THE WAVE COULD DEVELOP A LOW PRESSURE CIRCULATION,
POSSIBLY IN THE NORTHERN CARIBBEAN OR THE SOUTHWEST ATLANTIC. THIS
WAVE, WHICH IS CURRENTLY LOCATED AT 55W, HAS A 50% CHANCE OF
TROPICAL CYCLONE DEVELOPMENT IN THE NEXT SEVEN DAYS, PER THE
LATEST NATIONAL HURRICANE CENTER ADVISORY. NHC IS ALSO FOLLOWING
ANOTHER WAVE FURTHER EAST, AT 41W, WHICH HAS A 80% CHANCE OF
DEVELOPING INTO A TROPICAL CYCLONE, WHICH MAY BECOME OF INTEREST
LATE IN THE WEEK AND OVER THE WEEKEND.
TROPICAL SOUTH AMERICA:
IN SOUTH AMERICA, DAILY LOCALIZED CONVECTION IS EXPECTED TO
CONTINUE ON TUESDAY AFTER THE DEPARTURE OF DRIER AIR THROUGHOUT
MUCH OF THE NORTHERN CONTINENT LATER TONIGHT. INFLUENCE OF THE
PANAMANIAN LOW WILL CONTINUE TO BRING MOISTURE AND RAINFALL INTO
THE WEST COAST OF COLOMBIA AND ECUADOR EACH DAY IN THE FORECAST
PERIOD. BEGINNING ON TUESDAY, MOISTURE WILL RETURN TO THE INTERIOR
OF SOUTH AMERICA, AND SEASONABLE RAINFALL WILL RESTART, WITH THE
HIGHEST TOTALS IN PARTS OF PERU, COLOMBIA, ECUADOR, AND NORTHWEST
BRAZIL.
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 20N 39W 43W 45W 48W 51W 54W 56W 58W 60W
TW 22N 54W 56W 58W 60W 63W 66W 69W 70W 71W
TW 17N 83W 86W 89W 92W 95W DISS --------------
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