Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
218 PM EST TUE DEC 12 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 12/06
UTC: BROAD POLAR TROUGH EXTENDS FROM THE CENTRAL USA TO THE
WESTERN ATLANTIC...WITH AXIS BOTTOMING OUT NORTH OF 20N. ALSO AT
MID LEVELS...A LOW AMPLITUDE RIDGE EXTENDS WEST-TO-EAST ACROSS THE
CARIBBEAN BASIN...FAVORING A FAIRLY STRONG TRADE WINDS CAP ACROSS
THE EASTERN CARIBBEAN ISLES. AT LOW LEVELS...THE TROUGH ALOFT
SUSTAINS A SURFACE FRONT THAT STRETCHES ACROSS THE BAHAMAS-CUBA TO
THE WESTERN CARIBBEAN. OVER THE EASTERN CARIBBEAN...IN RESPONSE TO
THIS FEATURE...A LIGHT MEANDERING FLOW DOMINATES.

GLOBAL MODELS FORECAST A CLIPPER TO STREAM ACROSS THE EASTERN USA
LATER THIS AFTERNOON. AS IT ROUNDS THE BASE OF THE LONG WAVE
TROUGH NORTH OF THE ISLANDS...IT IS TO PRESS AGAINST THE MID LEVEL
RIDGE TO THE SOUTH. UNDER PRESSURE...THE RIDGE IS TO RELAX ITS
FOOTHOLD ACROSS THE EASTERN CARIBBEAN...WITH STRONG TRADE WINDS
CAP LIFTING ABOVE 700 HPA BY MIDDAY ON WEDNESDAY. DURING THAT
PERIOD THE PWAT CONTENT IS TO PEAK AROUND 1.25 INCHES. THE
SLIGHTLY MORE FAVORABLE ENVIRONMENTAL CONDITIONS...HOWEVER...WILL
BE SHORT LIVED. ON THURSDAY-FRIDAY MID LEVEL RIDGE PATTERN BOUNCES
BACK...STRENGTHENING THE TRADE WINDS CAP ACROSS THE CARIBBEAN
WHILE SUSTAINING A DRYING TREND. AT LOW LEVELS...THE POLAR FRONT
SLOWLY MOVES ACROSS THE TURKS AND CAICOS TO NORTHERN HISPANIOLA ON
WEDNESDAY MORNING. BUT AS IT LOSES ITS UPPER LEVEL
SUPPORT...FRONTAL BOUNDARY IS TO THEN GRADUALLY WEAKEN WHILE
RETROGRESSING ACROSS THE BAHAMAS-CUBA LATER IN THE WEEK. EVOLVING
LOW/MID LEVEL PATTERN TO THE WEST AND NORTH WILL HAVE AN INFLUENCE
ON THE LOCAL FLOW PATTERN. EARLY THIS MORNING THE STEERING FLOW
BECOME SLIGHTLY BETTER DEFINED AS THE WINDS  VEER TO THE
SOUTH-SOUTHEAST...SHIFTING TO THE SOUTH-SOUTHWEST LATER IN THE
DAY/EARLY WEDNESDAY MORNING. ON THURSDAY-FRIDAY...AS A RIDGE
GRADUALLY BUILDS TO THE NORTH...THE PREVAILING EASTERLY TRADES
RETURN TO THE FORECAST AREA. STRONGER WINDS ARE EXPECTED BY THE
END OF THE WEEK.

AS THE WINDS VEER TO THE SOUTH...EXPECTING SLIGHT INCREASE IN
DIURNAL CONVECTION ALONG THE CORDILLERA-NORTHERN PUERTO RICO
DURING THE DAY TODAY. SLIGHTLY HIGHER AMOUNTS ARE EXPECTED ON
WEDNESDAY AS THE MID LEVEL RIDGE PATTERN WEAKENS AND DEEPER
MOISTURE POOLS ACROSS THE FORECAST AREA. ON THURSDAY AND ONWARD
EXPECTING A LULL IN ACTIVITY...WITH EARLY MORNING TRADE WIND
SHOWERS OVER THE VIRGIN ISLES-EASTERN PUERTO RICO TO ONLY TRIGGER
LIGHT RAINFALL AMOUNTS. LIKEWISE ACROSS WESTERN INTERIOR PORTIONS
OF PUERTO RICO IN AFTERNOON CONVECTION.





TROPICAL DISCUSSION FROM DEC 12/12 UTC: A ROBUST UPPER RIDGE IS
ESTABLISHED ACROSS MOST OF THE CARIBBEAN BASIN WHILE CENTERING
OVER NORTHERN COLOMBIA/SOUTHERN CARIBBEAN. THIS RIDGE WILL LIMIT
THE PROGRESSION OF MID-LATITUDE TROUGHS AND ASSOCIATED SURFACE
FRONTS INTO THE BASIN. REGIONS PRONE TO UPPER TROUGH
INTENSIFICATION WILL LIMIT TO EXTREME WESTERN MEXICO AND THE
CENTRAL PORTIONS OF THE TROPICAL NORTH ATLANTIC.

A SURFACE FRONT IS LINGERING ACROSS THE NORTHWESTERN CARIBBEAN. AS
THE ASSOCIATED TROUGH HAS LIFTED INTO THE NORTH ATLANTIC...THE
FRONT IS REMAINING MOSTLY STATIONARY AND WEAKENING. YET...AS
ANOTHER STRONG UPPER TROUGH EXITS THE EAST COAST OF THE UNITED
STATES ON TUESDAY...NORTHERLY WINDS WILL INTENSIFY INTO WEDNESDAY
TO PRODUCE A TRANSIENT INTENSIFICATION OF THE AFOREMENTIONED
FRONT. YET...AS THIS SECOND UPPER TROUGH LIFTS ON THURSDAY AND
MID-UPPER RIDGE PATTERN ESTABLISHES OVER THE CENTRAL AND NORTHERN
CARIBBEAN BASIN...EXPECTING THE SURFACE FRONT TO RAPIDLY WEAKEN
DURING THURSDAY AND INTO FRIDAY. BY TUESDAY EVENING...THE
STATIONARY FRONT WILL EXTEND ACROSS THE SOUTHEASTERN
BAHAMAS...NORTHERN HAITI...JAMAICA INTO NORTHERN NICARAGUA. GIVEN
THE INTENSIFICATION OF THE NORTHERLIES LATE ON TUESDAY/EARLY
WEDNESDAY...THE FRONT WILL ADVANCE SLIGHTLY ACROSS NORTHERN
HISPANIOLA AS A COLD FRONT. BY WEDNESDAY EVENING...IT IS FORECAST
TO EXTEND JUST TO THE SOUTHEAST OF THE TURKS AND CAICOS
ISLANDS...THE NORTHERN DOMINICAN REPUBLIC...CENTRAL
HAITI...JAMAICA...WITH AN ILL-DEFINED TAIL INTO NORTHERN
NICARAGUA. AS THE NORTHERLY WINDS INCREASE TEMPORARILY...SHEAR
LINE CONVERGENCE WILL ALSO INCREASE ON WEDNESDAY. THIS WILL REFORM
THE SHEAR LINE ACROSS THE CENTRAL-WESTERN CARIBBEAN...BUT THE
FEATURE WILL LOSE DEFINITION DURING THURSDAY MORNING. BY THURSDAY
EVENING...THE FRONT WILL BECOME STATIONARY ONCE AGAIN ACROSS/JUST
TO THE SOUTHEAST OF THE TURKS AND CAICOS AND INTO THE WINDWARD
PASSAGE. THE WESTERN TIER OF THE FRONT WILL RETURN AS A WEAKENING
WARM FRONT TO EXTEND ACROSS THE SOUTHEAST OF THE CAYMAN ISLANDS
AND INTO THE HONDURAS/NICARAGUA BORDER. A SECOND FRONT WILL ALSO
ARRIVE IN THE BASIN...BUT IT WILL EXERT LIMITED EFFECTS IN
PRECIPITATION AS DEEP-LAYER MOISTURE REMAINS IN THE CENTRAL
CARIBBEAN. THE NEW FRONT WILL EXTEND ACROSS THE CENTRAL FLORIDA
PENINSULA INTO NORTHERN TAMAULIPAS IN MEXICO BY TUESDAY EVENING.
BY WEDNESDAY EVENING IT WILL EXTEND ACROSS THE CENTRAL BAHAMAS
INTO CENTRAL CUBA. DURING THURSDAY...IT WILL MERGE WITH THE
AFOREMENTIONED FRONT TO SUSTAIN THE BOUNDARY ALONG THE TURKS AND
CAICOS-SOUTHEASTERN CUBA.

IN TERMS OF PRECIPITATION IN ASSOCIATION WITH THE FRONTS AND SHEAR
LINE...LARGEST ACCUMULATIONS ARE EXPECTED IN NORTHERN SLOPES OF
JAMAICA ON TUESDAY-EARLY WEDNESDAY...WHERE ENHANCED MOISTURE
CONVERGENCE WILL PRODUCE 10-15MM/DAY AND MAXIMA OF 20-45MM. IN
SOUTH EASTERN CUBA...NORTHWESTERN HAITI AND THE SOUTHEASTERN
BAHAMAS/TURKS AND CAICOS...EXPECTING 10-15MM/DAY AND MAXIMA OF
20-35MM. POST-FRONTAL COLD AIR CUMULUS WILL CONTINUE STIMULATING
PRECIPITATION IN NORTHERN HONDURAS...WHERE EXPECTING 10-15MM/DAY
AND MAXIMA OF 20-35MM...WHILE IN SOUTHERN VERACRUZ/TABASCO
EXPECTING 05-10MM/DAY AND MAXIMA OF 15-20MM. SHOWERS PRODUCED BY
THE COLD AIR CUMULUS ARE TO RAPIDLY DECREASE IN INTENSITY DURING
THE DAY ON WEDNESDAY. ALSO ON TUESDAY-WEDNESDAY...CONVERGENCE
AHEAD OF A NORTHERLY LOW-LEVEL JET WILL CONTINUE STIMULATING
MOISTURE CONVERGENCE IN THE CARIBBEAN COAST OF COSTA RICA AND
WESTERN PANAMA...WHERE EXPECTING 15-20MM/DAY AND MAXIMA OF
25-50MM. BY WEDNESDAY-THURSDAY...LARGEST ACCUMULATIONS WITH THE
FRONT ARE EXPECTED IN THE NORTHERN DOMINICAN REPUBLIC...WHERE
ENHANCED MOISTURE CONVERGENCE WILL LEAD TO 15-20MM/DAY AND MAXIMA
OF 30-60MM. ACROSS WESTERN HAITI AND JAMAICA...WANING FRONTAL
CONVECTION WILL LEAD TO 10-15MM/DAY AND MAXIMA OF 20-30MM.
MOISTURE CONVERGENCE IN COSTA RICA AND WESTERN PANAMA WILL PRODUCE
10-15MM/DAY AND MAXIMA OF 20-40MM. BY THURSDAY-FRIDAY...EXPECTING
A SIGNIFICANT DECREASE IN ACCUMULATIONS AS THE SURFACE FRONT
WEAKENS...AND THE MID-LEVEL RIDGE PATTERN STRENGTHENS OVER THE
NORTHERN ANTILLES. DURING THIS PERIOD...FRONTAL CONVECTION WILL
LEAD TO AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM IN THE TURKS AND
CAICOS/SOUTHEASTERN BAHAMAS INTO NORTHERN HAITI. ACROSS NORTHERN
JAMAICA AND SOUTHEASTERN CUBA EXPECTING 00-05MM/DAY AND MAXIMA OF
10MM. AS THE EASTERLY TRADES REESTABLISH...MOISTURE WILL RETURN
INTO NORTHEASTERN NICARAGUA...WHERE IT WILL LEAD TO 05-10MM/DAY
AND MAXIMA OF 15-20MM. ALSO ON THURSDAY-FRIDAY...WANING MOISTURE
CONVERGENCE IN COSTA RICA WILL LEAD TO 10-15MM/DAY AND MAXIMA OF
20-35MM.

ALSO IN THE NORTHERN PART OF THE FORECAST DOMAIN...MODELS ARE
SHOWING UPPER TROUGH ORGANIZING OFF THE COAST OF WESTERN MEXICO.
THIS WILL INTERACT WITH A SUBTROPICAL MOISTURE PLUME THAT
ORIGINATES IN THE TROPICAL PACIFIC...AND SUSTAIN SIGNIFICANT
FORCING TO STIMULATE RAINFALL ON THURSDAY THROUGH SATURDAY.
ALTHOUGH DISCREPANCIES ON MODEL SOLUTIONS START APPEARING
THURSDAY...THE PATTERN WILL LIKELY PRODUCE MODERATE RAINFALL IN
THE SIERRA MADRE OCCIDENTAL OF SINALOA AND NAYARIT...WHERE
OROGRAPHIC UPLIFT WILL ENHANCE ACTIVITY LOCALLY. BY
THURSDAY-FRIDAY EXPECTING 10-15MM/DAY AND MAXIMA OF 20-40MM...WITH
THE POTENTIAL FOR A SLIGHT INCREASE ON FRIDAY-SATURDAY.

IN NORTHERN SOUTH AMERICA AND THE WINDWARD ISLANDS...A
TUTT-INDUCED WAVE IS APPROACHING THE REGION AND IS FORECAST TO
ORGANIZE AS IT CROSSES NORTHERN VENEZUELA ON WEDNESDAY AND
THURSDAY. THIS WILL LEAD TO A TRANSIENT INCREASE IN TRADE WIND
SHOWERS AND RAINFALL ACCUMULATIONS (SEE BELOW). IN COLOMBIA...AS A
DRY AIR MASS ARRIVES FROM THE EAST...EXPECTING A GRADUAL DECREASE
IN ACCUMULATIONS. INITIALLY...EXPECTING 10-15MM/DAY AND MAXIMA OF
20-30MM ACROSS THE CHOCO/EJE CAFETERO...DECREASING TO 00-05MM/DAY
AND ISOLATED MAXIMA OF 10MM DURING WEDNESDAY. A SLIGHT INCREASE IS
EXPECTED ON THURSDAY AS AN EASTERLY WAVE APPROACHES.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL  24   36   48   60   72   84   96     TYPE        SOF
59W     62W  66W  69W  73W   76W  80W  83W   TUTT INDCD/EW   10N

A TUTT-INDUCED WAVE IN THE WESTERN ATLANTIC IS STARTING TO
PROPAGATE AS AN EASTERLY WAVE. THIS WAVE WILL SLOWLY REGAIN
DEFINITION AS IT PROPAGATES ACROSS THE SOUTHERN CARIBBEAN. IT WILL
STIMULATE PRECIPITATION IN TRINIDAD AND TOBAGO/NORTHERN GUYANA ON
TUESDAY...WHERE IT WILL PRODUCE 05-10MM/DAY AND MAXIMA OF 15MM.
SIMILAR AMOUNTS WILL EXPAND INTO CENTRAL VENEZUELA ON WEDNESDAY.
DURING THURSDAY...SHOWERS WILL EXPAND INTO NORTHWESTERN
VENEZUELA/ABC...BUT EXPECTING A DECREASING TREND IN ACCUMULATIONS
TO 00-05MM/DAY AND MAXIMA OF 10MM.

GORDON...NMS (BELIZE)
PECK...MS (JAMAICA)
RIVAS...SENAMHI (PERU)
GALVEZ/DAVISON...WPC (USA)

$$





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