Prognostic Meteorological Discussion
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FXCA20 KWBC 251835
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 PM EDT MON SEP 25 2017

TROPICAL DISCUSSION FROM SEP 25/12 UTC: POTENT POLAR TROUGH ACROSS
THE WESTERN UNITED STATES WILL HAVE A STRONG INFLUENCE IN MOIST
CONVECTION AND PRECIPITATION ACROSS NORTHERN MEXICO. THE TROUGH
WILL BE ACCOMPANIED BY AN UPPER JET...WHICH WILL POSITION ITS
DIVERGENT ENTRANCE OVER COAHUILA DURING TUESDAY INTO EARLY
WEDNESDAY. THIS TROUGH AND UPPER JET WILL INTERACT WITH A MOIST
PLUME THAT ORIGINATES IN THE NORTHERN GULF OF MEXICO. THE
INTERACTION BETWEEN THE MOIST PLUME AND THE UPPER DYNAMICS WILL
RESULT IN MODERATE RAINFALL AMOUNTS THROUGH THE CYCLE. BY
MONDAY-EARLY TUESDAY...EXPECTING RAINFALL ACCUMULATIONS OF
15-30MM/DAY AND MAXIMA OF 40-80MM. BY TUESDAY-WEDNESDAY THIS IS TO
INCREASE TO 20-40MM/DAY AND MAXIMA OF 50-100MM. THIS IS DECREASING
TO 15-20MM/DAY AND MAXIMA OF 25-50MM.

ALSO IN MEXICO...THE REMNANTS OF TROPICAL STORM PILAR ARE TO
PRODUCE LOCALLY HEAVY RAINS IN NAYARIT AND SOUTHERN
SINALOA/WESTERN JALISCO ON MONDAY...WHERE EXPECTING 15-20MM/DAY
AND MAXIMA OF 35-70MM. AMOUNTS WILL DECREASE RAPIDLY AFTER.

STRONG TUTT IS FORECAST TO SLOWLY MEANDER FROM THE NORTHEASTERN
GULF OF MEXICO INTO THE FLORIDA PENINSULA FROM MONDAY THROUGH
THURSDAY. THIS SYSTEM HAS A REFLECTION INTO THE MID-LEVELS OF THE
TROPOSPHERE...AND IS DRAWING THE ITCZ AND TROPICAL MOISTURE
NORTHWARD ACROSS THE WESTERN CARIBBEAN. WHILE THE TUTT
MEANDERS...A CORRIDOR OF ENHANCED MOISTURE CONVERGENCE WILL
CONTINUE ORGANIZING ACROSS THE WESTERN CARIBBEAN AND GULF OF
HONDURAS...AND IS FORECAST TO EXTEND NORTH INTO MOST OF CUBA AND
THE CAYMAN ISLANDS. THIS PATTERN WILL FAVOR SEVERAL DAYS WITH
HEAVY RAINFALL IN THESE REGIONS. THROUGH EARLY TUESDAY...LARGEST
ACCUMULATIONS ARE EXPECTED IN NORTHEASTERN HONDURAS/NORTHEASTERN
NICARAGUA AND ALONG EASTERN PORTIONS OF THE YUCATAN
PENINSULA/BELIZE...WHERE EXPECTING 15-20MM/DAY AND MAXIMA OF
30-60MM. BY TUESDAY-WEDNESDAY...EXPECTING LARGEST AMOUNTS IN THE
NORTHEASTERN YUCATAN PENINSULA...JAMAICA/CAYMAN ISLANDS AND MOST
OF CUBA...WHERE ACCUMULATIONS WILL REACH 15-30MM/DAY AND MAXIMA OF
40-80MM. BY WEDNESDAY-THURSDAY...EXPECTING 15-20MM/DAY AND MAXIMA
OF 25-50MM IN CENTRAL/WESTERN CUBA AND INTO THE CANCUN REGION.
ACROSS THE BAHAMAS...JAMAICA AND THE CAYMAN ISLANDS...EXPECTING
10-15MM/DAY AND MAXIMA OF 20-30MM.

ANOTHER REGION WHERE ACTIVE CONVECTION WILL CONTINUE IS CENTRAL
AMERICA AND SOUTHERN MEXICO. MODELS CONTINUE INDICATING THE
PERSISTENCE OF THE ITCZ NEAR THE PACIFIC COAST THROUGH THE CYCLE.
WHILE PRECIPITABLE WATER REMAINS WELL OVER 50MM AND WESTERLY WINDS
CONTINUE...EXPECTING MOST ACTIVE CONVECTION TO CONTINUE CLUSTERING
ALONG THE PACIFIC BASIN AND CONTINENTAL DIVIDE THROUGH THE CYCLE.
LOCALLY HEAVY RAIN IS ALSO EXPECTED IN PARTS OF NORTHEASTERN
NICARAGUA AND HONDURAS EARLY IN THE CYCLE...IN ASSOCIATION WITH A
TROUGH/ENHANCED LOW-LEVEL MOISTURE CONVERGENCE. THROUGH EARLY
TUESDAY...LARGEST ACCUMULATIONS ARE EXPECTED ACROSS
CHIAPAS/SOUTHERN GUATEMALA EL SALVADOR...INTO WESTERN COSTA
RICA...WHERE AMOUNTS WILL REACH 15-20MM/DAY AND MAXIMA OF 25-50MM.
BY TUESDAY-EARLY WEDNESDAY...AMOUNTS WILL PEAK IN OAXACA/CHIAPAS
AND SOUTHERN GUATEMALA...AS SOUTHWESTERLY WINDS INCREASE OVER 15KT
AND LEAD TO A PEAK IN LOW-LEVEL MOISTURE CONVERGENCE. THIS WILL
RESULT IN 20-40MM/DAY AND MAXIMA OF 50-100MM. ELSEWHERE...BETWEEN
SOUTHERN GUATEMALA AND WESTERN PANAMA EXPECTING 10-15MM/DAY AND
MAXIMA OF 20-35MM. BY WEDNESDAY-THURSDAY...LARGEST ACCUMULATIONS
ARE EXPECTED ACROSS THE GULF OF TEHUANTEPEC
REGION/CHIAPAS/SOUTHERN GUATEMALA...WHERE AMOUNTS WILL REACH
15-20MM/DAY AND MAXIMA OF 35-70MM. AN INCREASE IN ONSHORE FLOW
ACROSS THE SOUTHERN GULF OF MEXICO WILL INCREASE OROGRAPHIC UPLIFT
IN VERACRUZ...WHERE EXPECTING 10-15MM/DAY AND MAXIMA OF 20-40MM.

WHILE ACTIVE CONVECTION CONTINUES ACROSS THE WESTERN CARIBBEAN AND
CENTRAL AMERICA...THE EASTERN CARIBBEAN IS EXPECTING MUCH DRIER
CONDITIONS...AS A DRY AIR MASS ARRIVES FROM THE TROPICAL ATLANTIC
ON MONDAY. THIS WILL SUSTAIN A DECREASE IN ACCUMULATIONS ACROSS
THE ARC OF THE LESSER ANTILLES AND PUERTO RICO-HISPANIOLA INTO THE
SOUTHEASTERN BAHAMAS THROUGH THE FORECAST CYCLE. AT UPPER
LEVELS...A SYSTEM OF INTEREST IS A TUTT THAT IS FORECAST TO
MEANDER WESTWARD FROM 22N-24N 55W ON MONDAY EVENING TO THE VIRGIN
ISLANDS/EASTERN CARIBBEAN BY WEDNESDAY-THURSDAY. THIS TUTT IS
INDUCING A WAVE IN THE TRADES (SEE BELOW) THAT WILL SERVE AS A
REGION OF LOW-LEVEL MOISTURE CONVERGENCE...WHILE ENTERING THE
WINDWARD ISLANDS LATE ON WEDNESDAY. THE INTERACTION OF THE UPPER
DIVERGENT PATTERN IN THE SOUTHEASTERN PERIPHERY OF THE TUTT...WITH
THE TUTT-INDUCED WAVE AND THE ITCZ...WILL LEAD TO MODERATE
RAINFALL AMOUNTS IN THE ARC OF THE LESSER ANTILLES DURING
WEDNESDAY-THURSDAY...AND PUERTO RICO/USVI ON THURSDAY-FRIDAY. IN
THE MEAN TIME...ON MONDAY...LARGEST ACCUMULATIONS ARE EXPECTED IN
ASSOCIATION WITH ITCZ CONVERGENCE IN TRINIDAD AND
TOBAGO/NORTHEASTERN VENEZUELA...WHERE EXPECTING 10-15MM/DAY AND
MAXIMA OF 20-30MM. BY TUESDAY-WEDNESDAY...EXPECTING 10-15MM/DAY
AND MAXIMA OF 20-35MM EXTENDING WEST INTO NORTHERN VENEZUELA. BY
WEDNESDAY-THURSDAY...EXPECTING 10-15MM/DAY AND MAXIMA OF
20-30MM/DAY FROM TRINIDAD AND TOBAGO NORTH INTO SAINT LUCIA AND
BARBADOS...UNDER THE INFLUENCE OF THE ARRIVING TUTT-INDUCED WAVE
AND VENTILATION FROM THE TUTT TO THE NORTH.

ACROSS NORTHERN SOUTH AMERICA...ACTIVITY WILL BE MOSTLY MODULATED
BY THE NET AND THE DIURNAL CYCLE OF RADIATION. LARGEST
ACCUMULATIONS ARE EXPECTED IN WESTERN COLOMBIA ON
MONDAY-TUESDAY...WERE ONSHORE FLOW AST LOW-LEVELS WILL LEAD TO
15-20MM/DAY AND MAXIMA OF 25-50MM. AMOUNTS WILL DECREASE AFTER.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24    36    48    60    72    84    96   TYPE  SOF
36W      39W   43W   48W   52W   55W   60W   64W   TUTT-INDCD 23N
63W      66W   70W   73W   77W   81W   84W   87W   TW    19N

A TUTT-INDUCED WAVE IS INITIALIZED AT 36W. THIS WAVE IS FORECAST
TO ENTER GUIANAS ON WEDNESDAY...WHERE IT WILL LEAD TO
ACCUMULATIONS OF 05-10MM/DAY AND MAXIMA OF 15MM. THE WAVE WILL
HAVE A STRONGER IMPACT ON THE WINDWARD ISLANDS/NORTHEASTERN
VENEZUELA AND TRINIDAD AND TOBAGO ON THURSDAY...AS IT INTERACTS
WITH THE ITCZ AND WITH VENTILATION FROM THE TUTT TO THE NORTHWEST.
HERE...IT WILL LEAD TO ACCUMULATIONS OF 10-15MM/DAY AND MAXIMA OF
20-30MM.

TROPICAL WAVE ALONG 63W AND SOUTH OF 19N HAS A STRONGER SIGNATURE
AT 700 HPA THAN AT 850 HPA. THIS WAVE WILL ENHANCE ACTIVITY ACROSS
PUERTO RICO ON MONDAY...WHERE IT WILL LEAD TO ISOLATED MAXIMA OF
15MM. IT WILL ALSO ENHANCE ACCUMULATIONS IN CENTRAL AND WESTERN
VENEZUELA...WHERE IT WILL LEAD TO 10-15MM/DAY AND MAXIMA OF
20-30MM ON MONDAY. ON TUESDAY...THIS WILL LEAD TO 10-15MM/DAY AND
MAXIMA OF 20-40MM IN NORTHERN COLOMBIA...WHILE IN SOUTHERN AND
SOUTHWESTERN VENEZUELA EXPECTING 10-15MM/DAY AND MAXIMA OF
20-30MM. AMOUNTS ARE TO DECREASE AFTER TO 05-10MM/DAY AND MAXIMA
OF 15-25MM.

GUY...NMS (BELIZE)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)

$$





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