301  
FXCA20 KWBC 131931  
PMDCA  
 
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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