399
FXCA20 KWBC 181757
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1257 PM EST THU DEC 18 2025
FORECAST BULLETIN 18 DECEMBER 2025 AT 1750 UTC:
THE BAHAMAS AND CARIBBEAN:
A COLD FRONT IS EXPECTED TO APPROACH THE BAHAMAS LATER TODAY INTO
FRIDAY. AS THE COLD FRONT APPROACHES, LOW-LEVEL CONVERGENCE IS
EXPECTED TO INCREASE BRINGING MORE MOISTURE INTO THE REGION. AN
ENHANCEMENT IN UPPER-LEVEL DIVERGENCE IS ALSO EXPECTED TODAY AS A
MID-LATITUDES UPPER-LEVEL TROUGH, REFLECTED AT MID-LEVELS,
APPROACHES THE REGION. THESE CONDITIONS WILL CONTRIBUTE TO THE
PRECIPITATION OVER THE AREA. ACCUMULATIONS BETWEEN 15MM-20MM ARE
EXPECTED. AS THE COLD FRONT AND THE UPPER-LEVEL TROUGH CONTINUE TO
PROPAGATE EASTWARD, UPPER-LEVEL CONFLUENCE AND LOW-LEVEL
DIVERGENCE ARE EXPECTED TO INCREASE OVER THE BAHAMAS, LIMITING
PRECIPITATION FROM FRIDAY THROUGH SATURDAY.
THE PRESENCE OF AN UPPER-LEVEL RIDGE REFLECTED AT MID-LEVEL HIGH
NORTH OF THE HISPANIOLA TODAY, IS LIKELY TO LIMIT THE CONVECTIVE
ACTIVITY OVER THE REGION. THE HIGH IS EXPECTED TO WEAKEN OVER THE
ATLANTIC AS THE MID-LATITUDE UPPER LEVEL TROUGH APPROACHES THE
ATLANTIC, BUT UPPER-LEVEL RIDGING IS EXPECTED TO REMAIN OVER THE
CARIBBEAN THROUGHOUT THE FORECAST PERIOD. THIS IS GOING TO INHIBIT
THE DEVELOPMENT OF CONVECTIVE ACTIVITY IN THE REGION. LIGHT
PRECIPITATION IS EXPECTED EACH DAY OVER THE REGION, MOSTLY DUE TO
THE PRESENCE OF LOW-LEVEL TROUGHS INCREASING LOW-LEVEL MOISTURE
CONVERGENCE. FROM TODAY THROUGH FRIDAY RAINFALL IS FORECASTED OVER
THE LESSER ANTILLES AND PUERTO RICO WITH A LOW-LEVEL TROUGH
MOVING INTO THE AREA, LEAVING ACCUMULATIONS AROUND 15MM THE
LOW-LEVEL TROUGH IS THEN EXPECTED TO REACH HISPANIOLA AND BRING
SOME PRECIPITATION OVER THE AREA FROM FRIDAY THROUGH SATURDAY.
FROM SATURDAY THROUGH SUNDAY, THE LOW-LEVEL FLOW OVER THE EASTERN
CARIBBEAN IS EXPECTED TO BECOME MORE EASTERLY, FAVORING THE
DEVELOPMENT OF PASSING SHOWERS. MOST OF THE PRECIPITATION IS
EXPECTED TO HAPPEN OVER THE LESSER ANTILLES, AS ANOTHER LOW-LEVEL
TROUGH ENTERS THE AREA BRINGING SOME MOISTURE. ACCUMULATIONS,
HOWEVER, ARE FORECASTED TO REMAIN RELATIVE LOW WITH A MAXIMA OF
15MM.
MEXICO AND CENTRAL AMERICA:
RAINFALL AND THUNDERSTORMS ARE EXPECTED TODAY THROUGH FRIDAY
MORNING OVER GUATEMALA AND BELIZE, AND PORTIONS OF HONDURAS AND EL
SALVADOR. THE MAIN DRIVERS OF THE PRECIPITATION ARE A LOW-LEVEL
TROUGH OVER THE AREA, A MID-LEVEL SHORTWAVE TROUGH OVER LAND WITH
VORTICITY, AND A SHORTWAVE UPPER-LEVEL TROUGH WEST OF CENTRAL
AMERICA THAT IS FORECASTED TO INCREASE UPPER-LEVEL DIVERGENCE
MAINLY OVER GUATEMALA. RAINFALL ACCUMULATIONS ARE FORECASTED TO BE
AROUND 20-35MM, WITH ISOLATED HIGHER VALUES. ADDITIONAL 20-35MM
ARE EXPECTED OVER REGIONS OF GUATEMALA FROM FRIDAY THROUGH
SATURDAY WITH SOME LOW-LEVEL TROUGHING REMAINING IN THE AREA, BUT
THE HEAVIEST PRECIPITATION IS EXPECTED OVER SOUTHERN MEXICO WITH
THE PRESENCE OF A LOW-LEVEL TROUGH INCREASING THE LOW-LEVEL FLOW
INTO MEXICO. SOME UPPER-LEVEL SUPPORT IS ALSO ACCEPTED WITH AN
UPPER LEVEL TROUGH INCREASING DIFFLUENCE OVER SOUTHERN MEXICO, AND
A MID-LEVEL TROUGH OVER YUCATAN INCREASING INSTABILITY. MORE QUIET
CONDITIONS ARE EXPECTED FROM SATURDAY THOUGH SUNDAY OVER CENTRAL
AMERICA. LOW-LEVEL TROUGHS ARE FORECASTED TO BRING SOME
PRECIPITATION INTO BELIZE AND THE EASTERN COAST OF NICARAGUA, FROM
SATURDAY THROUGH SUNDAY. MAXIMA RAINFALL ACCUMULATIONS ARE
EXPECTED TO BE AROUND 15-25MM. RAINFALL IS LIKELY TO HAPPEN EACH
DAY OVER COSTA RICA AND PANAMA WITH THE PRESENCE OF THE MONSOON AS
IT CONTINUES TO PROVIDE CIRCULATION OVER THE REGION.
TROPICAL SOUTH AMERICA:
OVER SOUTH AMERICA, PRECIPITATION IS EXPECTED EACH DAY OVER THE
PACIFIC COAST OF COLOMBIA AND PORTIONS OF ECUADOR, WITH THE
LOW-LEVEL FLOW BRINGING MOISTURE FROM THE PACIFIC OCEAN OVER LAND
AS A LOW-LEVEL TROUGH DEVELOPS OVER THE PACIFIC. TOTAL MAXIMA
ACCUMULATIONS, HOWEVER, ARE NOT EXPECTED TO EXCEED 35MM, AS THE
FLOW IS RELATIVELY WEAK. ANOTHER REGION THAT IS EXPECTED TO
RECEIVE PRECIPITATION EACH DAY THROUGHOUT THE FORECAST PERIOD IS
NORTHEASTERN BRAZIL, FRENCH GUIANA AND SURINAME DUE TO THE
PRESENCE OF THE ITCZ, STRONG LOW-LEVEL FLOW AND MOISTURE ADVECTION
INTO THE REGION. THE NOCTURNAL JET OVER SOUTH AMERICA IS EXPECTED
TO BRING A DRYING TREND OVER NORTH SOUTH AMERICA, LIMITING
PRECIPITATION OVER PORTIONS OF COLOMBIA AND VENEZUELA THROUGHOUT
THE FORECAST PERIOD. LIGHT RAINFALL IS LIKELY OVER THE CARIBBEAN
COAST OF THE REGION MOSTLY DUE TO MOISTURE ADVECTION, LOW-LEVEL
MOISTURE CONVERGENCE AND LOCAL EFFECTS. AN AREA OF INTEREST FOR
TODAY IS NORTHEASTERN ECUADOR AND NORTHERN PERU AS AN ENHANCEMENT
IN LOW-LEVEL CONVERGENCE IS FORECASTED, AND THE NOCTURNAL
LOW-LEVEL JET IS EXPECTED TO ADVECT MOISTURE INTO THAT REGION.
FROM FRIDAY THROUGH SATURDAY THESE CONDITIONS ARE FORECASTED TO
CONTINUE PRECIPITATION OVER ECUADOR, BUT PRECIPITATION IS EXPECTED
TO DECREASE FROM SATURDAY THROUGH SUNDAY AS MOISTURE DECREASES IN
THE REGION. MOST OF THE PRECIPITATION THROUGHOUT THE FORECAST
PERIOD IS EXPECTED TO HAPPEN OVER BRAZIL. THE MAIN DRIVERS OF
PRECIPITATION WILL BE LOW-LEVEL MOISTURE CONVERGENCE, THE PRESENCE
OF LOW-LEVEL TROUGHS AND UPPER-LEVEL DIFFLUENCE.
POSITIONS OF TROPICAL/EASTERLY WAVES INITIALIZED AT 12 UTC
TYP SOF INIT 19/00 19/12 20/00 20/12 21/00 21/12 22/00
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