Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM EST WED DEC 13 2017

TROPICAL DISCUSSION FROM DEC 13/12 UTC: A ROBUST UPPER RIDGE
CENTERS OVER MOST OF THE CARIBBEAN...AND HAS ALSO A REFLECTION
INTO THE MID-LEVELS. AS RIDGE PATTERN STRENGTHENS THROUGH THE
FORECAST CYCLE...EXPECTING A STRENGTHENING OF THE TRADE WIND CAP
ACROSS THE CARIBBEAN...WHICH WILL RESULT IN A GENERAL DECREASING
TREND IN ACCUMULATIONS.

IN THE MEAN TIME...TWO SURFACE FRONTS CONTINUE LINGERING ACROSS
THE NORTHWESTERN CARIBBEAN. AS THE ASSOCIATED UPPER TROUGHS LIFT
NORTHEAST ACROSS THE NORTH ATLANTIC...THE FRONTS ARE TO STOP
PROPAGATING SOUTHEASTWARD ON WEDNESDAY. AFTER THIS PERIOD THE
FRONTS WILL FRONTOLIZE AND TROPICAL MOISTURE WILL RETURN WESTWARD
INTO NORTHERN CENTRAL AMERICA. BY WEDNESDAY EVENING...SURFACE
FRONT WILL EXTEND ACROSS NORTHERN HISPANIOLA...WESTERN
JAMAICA...INTO SAN ANDRES/NUEVA PROVIDENCIA. ALSO...A SECOND FRONT
WILL EXTEND ACROSS THE CENTRAL BAHAMAS INTO CENTRAL CUBA...BUT IT
WILL LOSE DEFINITION OVERNIGHT AS IT PROPAGATES TO THE SOUTHEAST.
BY THURSDAY EVENING...A WEAKENING WARM FRONT WILL EXTEND ACROSS
THE SOUTHEASTERN BAHAMAS-SOUTHEASTERN CUBA INTO THE CAYMAN
ISLANDS. THIS FRONT WILL RAPIDLY FRONTOLIZE INTO FRIDAY
EVENING...WHEN AN ILL-DEFINED BOUNDARY IS FORECAST TO EXTEND
ACROSS THE CENTRAL BAHAMAS-CENTRAL CUBA...NORTH OF THE CAYMAN
ISLANDS. LARGEST RAINFALL ACCUMULATIONS WITH THESE SYSTEMS ARE
EXPECTED ON WEDNESDAY-EARLY THURSDAY. DURING THIS
PERIOD...MOISTURE CONVERGENCE AND OROGRAPHIC INTERACTIONS IN
NORTHERN HISPANIOLA WILL LEAD TO 15-20MM/DAY AND MAXIMA OF
30-60MM. IN COSTA RICA AND WESTERN PANAMA...CONTINUED MOISTURE
CONVERGENCE WILL LEAD TO 10-15MM/DAY AND MAXIMA OF 20-40MM IN
COSTA RICA/WESTERN PANAMA. ACROSS JAMAICA...HAITI INTO THE
WINDWARD PASSAGE EXPECTING 10-15MM/DAY AND MAXIMA OF 20-30MM. BY
THURSDAY-EARLY FRIDAY...FRONTOLYSIS WILL LEAD TO A MARKED DECREASE
IN ACCUMULATIONS. DURING THIS PERIOD...EXPECTING 05-10MM/DAY AND
MAXIMA OF 15MM ACROSS THE TURKS AND CAICOS/SOUTHEASTERN
BAHAMAS/SOUTHEASTERN CUBA...AND 00-05MM/DAY AND MAXIMA OF 10MM IN
NORTHERN JAMAICA-CAYMAN ISLANDS. ALSO...MOISTURE RETURN INTO THE
CARIBBEAN COAST OF NICARAGUA AND COSTA RICA WILL SUSTAIN
05-10MM/DAY AND MAXIMA OF 15-20MM.

IN MEXICO...A SUBTROPICAL MOISTURE PLUME/ATMOSPHERIC RIVER THAT
ORIGINATES IN THE TROPICAL PACIFIC...IS FORECAST TO INTERACT WITH
A STRONG UPPER TROUGH DIGGING ACROSS THE SOUTHWESTERN USA. THIS
WILL LEAD TO UNUSUALLY HEAVY PRECIPITATION IN
SINALOA/NAYARIT/DURANGO/ZACATECAS AND INTO OTHER PARTS OF
NORTH-CENTRAL MEXICO ON THURSDAY AND FRIDAY.
FURTHERMORE...VERTICAL MOTION WILL BE STIMULATED BY THE
ESTABLISHMENT OF THE DIVERGENT ENTRANCE OF AN UPPER JET. BY
THURSDAY-EARLY FRIDAY...EXPECTING 10-15MM/DAY AND MAXIMA OF
20-40MM IN SINALOA AND NAYARIT. INLAND INTO ZACATECAS/SAN LUIS
POTOSI EXPECTING 05-10MM/DAY AND MAXIMA OF 15-20MM. IN
CHIHUAHUA/COAHUILA EXPECTING 00-05MM/DAY AND MAXIMA OF 10MM. BY
FRIDAY SATURDAY...RAINFALL IS TO PEAK TO PRODUCE ACCUMULATIONS OF
15-20MM/DAY AND MAXIMA OF 25-50MM FROM SINALOA/NAYARIT NORTH INTO
COAHUILA AND SAN LUIS POTOSI.

ALSO IN MEXICO...ANOTHER FRONT WILL ARRIVE ON THURSDAY. BY
THURSDAY EVENING THE FRONT WILL EXTEND ACROSS NORTHERN TAMAULIPAS
INTO SOUTHERN COAHUILA AND EASTERN CHIHUAHUA. BY FRIDAY EVENING IT
WILL EXTEND ACROSS CENTRAL VERACRUZ. THE FRONT WILL STALL DURING
LATE FRIDAY TO THEN START RETREATING NORTHWARD ACROSS THE GULF OF
MEXICO ON SATURDAY...WHICH CONTRASTS WITH THE EVOLUTION OF THE
LATEST FRONTS. AS THE FRONT PROGRESSES ACROSS THE GULF COAST ON
FRIDAY IT WILL STIMULATE PRECIPITATION ALONG THE EASTERN COAST OF
MEXICO...WHERE EXPECTING 05-10MM/DAY AND MAXIMA OF 15MM.

IN CENTRAL AMERICA...AS THE FRONT WEAKENS TO THE EAST...EASTERLY
TRADE WINDS ARE TO RETURN DURING THURSDAY. THIS WILL BRING BACK
THE MOISTURE LINGERING OVER OPEN WATERS OF THE SOUTHERN CARIBBEAN.
AS MOISTURE RETURNS...EXPECTING RAINFALL ACCUMULATIONS OF
05-10MM/DAY AND MAXIMA OF 15-20MM ACROSS COSTA
RICA/NICARAGUA/NORTHERN HONDURAS ON THURSDAY-FRIDAY...AND SIMILAR
AMOUNTS SPREADING INTO BELIZE AND NORTHERN GUATEMALA/QUINTANA ROO
BY FRIDAY-SATURDAY. ALSO DURING THIS PERIOD...AN EASTERLY WAVE
WILL ARRIVE INTO THE CARIBBEAN COAST OF CENTRAL AMERICA TO PRODUCE
05-10MM/DAY AND MAXIMA OF 15-25MM. TRANSIENT WET PATTERN WILL
EXTEND INTO SUNDAY ACROSS BELIZE AND EASTERN PORTIONS OF THE
YUCATAN PENINSULA.

IN NORTHERN SOUTH AMERICA AND THE WINDWARD ISLANDS...CONVECTION IS
BEING MODULATED BY AN EASTERLY WAVE (SEE BELOW). OTHER THAN THIS
WAVE...A REGION OF INTEREST IS FRENCH GUIANA...WHERE AN ACTIVE
ATLANTIC ITCZ IS LEADING TO SEVERAL HEAVY-RAIN PRODUCING SHOWERS
AND THUNDERSTORMS. THROUGH EARLY THURSDAY EXPECTING 15-20MM/DAY
AND MAXIMA OF 40-80MM...DECREASING GRADUALLY AFTER.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL  24   36   48   60   72   84   96     TYPE     SOF
65W     68W  72W  76W  80W   83W  86W  89W    EW       10N

AN EASTERLY WAVE IS INITIALIZED AT 65W. THIS WAVE IS REGAINING
DEFINITION AS IT PROPAGATES ACROSS THE SOUTHERN CARIBBEAN. THROUGH
EARLY THURSDAY...IT WILL ENHANCE PRECIPITATION IN CENTRAL/NORTH
EASTERN VENEZUELA AND TRINIDAD AND TOBAGO...WHERE IT WILL LEAD TO
05-10MM/DAY AND MAXIMA OF 15MM. BY THURSDAY-FRIDAY...THIS WILL
LEAD TO 00-05MM/DAY AND MAXIMA OF 10MM IN NORTHERN VENEZUELA AND
THE ABC ISLANDS. BY FRIDAY-SATURDAY...THE WAVE WIL LEAD TO
05-10MM/DAY AND MAXIMA OF 15-25MM ACROSS SAN ANDRES/NUEVA
PROVIDENCIA INTO THE CARIBBEAN COAST OF COSTA RICA AND NICARAGUA.

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

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