281  
FXCA20 KWBC 231923  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
223 PM EST TUE JAN 23 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 23/06  
UTC: A MID LEVEL HIGH OVER THE DOMINICAN REPUBLIC ANCHORS A RIDGE  
OVER THE WESTERN ATLANTIC-NORTHEAST CARIBBEAN ISLES. THIS FAVORS A  
CONVERGENT/SUBSIDENT PATTERN ACROSS THE FORECAST AREA. ALTHOUGH  
THE HIGH RELOCATES TO THE BAHAMAS AS THE WEEK WEARS ON...THE RIDGE  
IS TO PERSIST AND THE ASSOCIATED TRADE WINDS CAP IS TO HOLD WITH  
AN ELEVATED CAP INVERSION IS TO PREVAIL THROUGH THE END OF THE  
WEEK.  
 
AT LOW LEVELS...A HIGH OVER BERMUDA ANCHORS A RIDGE OVER THE  
WESTERN ATLANTIC/ NORTHERN CARIBBEAN ISLANDS. A WANING FRONT  
BOUNDS THE SOUTHERN FRINGES OF THIS RIDGE...WITH BOUNDARY  
EXTENDING JUST NORTH OF THE GREATER ANTILLES. LACKING UPPER LEVEL  
SUPPORT...THE FRONT IS TO DISSIPATE DURING THE NEXT DAY OR SO.  
FURTHERMORE...UNDER PRESSURE FROM POLAR FRONT/TROUGH EXITING THE  
USA...THE LOW LEVEL RIDGE IS TO WEAKEN AS IT RELOCATES TO THE  
CENTRAL ATLANTIC EARLY IN THE CYCLE. AS THE PRESSURE GRADIENT  
SLACKENS...LIGHTER EASTERLY TRADES ARE TO PREVAIL THROUGH  
MIDMORNING ON FRIDAY. THE LIGHTER WINDS WILL ALLOW SHALLOW  
MOISTURE TO POOL ACROSS THE NORTHEAST CARIBBEAN...WITH PWAT  
CONTENT FORECAST TO PEAK AROUND 1.50 INCHES ON TUESDAY AFTERNOON  
THROUGH EARLY THURSDAY MORNING. THIS WILL FEED DIURNAL CONVECTION  
OVER THE FORECAST AREA ON TUESDAY AND WEDNESDAY. DURING THIS  
PERIOD THE NAM AND REGIONAL HRWRF SHOW POTENTIAL FOR MODERATE  
RAINFALL AMOUNTS ACROSS WESTERN PUERTO RICO. A DRYER AIR MASS IS  
TO THEN ENTRAIN FROM THE EAST ON THURSDAY...WITH LIGHT AFTERNOON  
CONVECTION TO LIMIT TO THE CORDILLERA/INTERIOR PORTIONS OF PUERTO  
RICO.  
 
LATER IN THE WEEK...POLAR FRONT EXITING THE EASTERN USA MOVES JUST  
NORTH OF THE FORECAST AREA ON FRIDAY...WITH THE BOUNDARY STALLING  
ALONG 22N/23N. AS THE FRONT MOVES ACROSS THE WESTERN ATLANTIC THIS  
WILL BE PRECEDED BY A PREFRONTAL SHEAR LINE. NOTE THAT IN THIS  
CYCLE THE GFS FAVORS A MORE DYNAMIC FEATURE...WITH THE SHEAR LINE  
MOVING OVER PUERTO RICO ON FRIDAY AND OVER THE LEEWARD ISLES LATER  
IN THE DAY/EARLY SATURDAY MORNING. MODELS CONTINUE TO FORECAST A  
FAIRLY STRONG TRADE WINDS SURGE TO ACCOMPANY THE SHEAR LINE AS IT  
ENTERS THE FORECAST AREA...WITH 850 HPA WINDS PEAKING AT 30-35KT.  
THIS WILL FAVOR A COLD ADVECTIVE PATTERN THAT IS TO ENHANCE  
CONVECTIVE DEVELOPMENT ON FRIDAY TO SATURDAY. SCATTERED SHOWERS  
ARE EXPECTED DURING THE DAY...WITH MOST ACTIVE CONVECTION  
AFFECTING THE NORTHERN VI AND THE SAN JUAN METRO AREA/NORTHERN  
HALF OF PUERTO RICO.  
 
TROPICAL DISCUSSION FROM JAN 23/12 UTC: IN MEXICO...AT UPPER  
LEVELS...A TROUGH EXTENDS AN AXIS OVER THE PACIFIC ALONG 112W.  
THIS IS INTERACTING WITH A MOIST TROPICAL PLUME AND ENHANCING DEEP  
CONVECTION JUST TO THE EAST OF ISLA SOCORRO IN THE PACIFIC...WHICH  
IS RESULTING IN PLENTY OF HIGH CLOUDS IN CENTRAL AND NORTHERN  
MEXICO. IN THE GULF OF MEXICO...A FRONT EXTENDS FROM THE FLORIDA  
PENINSULA INTO CENTRAL VERACRUZ. THIS IS LEADING TO SCATTERED  
CONVECTION MOSTLY IN THE GULF...BUT AFFECTING PARTS OF VERACRUZ  
AND TABASCO. THIS FRONT IS ASSOCIATED WITH AN UPPER TROUGH  
PROPAGATING TOWARDS THE EAST COAST OF THE UNITED STATES. THE FRONT  
WILL BE THE FEATURE OF INTEREST IN MEXICO AND NORTHERN CENTRAL  
AMERICA...AS IT WILL ENHANCE PRECIPITATION THROUGH THE FORECAST  
CYCLE. BY TUESDAY EVENING...THE FRONT WILL EXTEND FROM CENTRAL  
FLORIDA INTO THE SOUTHERN GULF OF CAMPECHE NEAR COATZACOALCOS. BY  
WEDNESDAY EVENING THE FRONT WILL EXTEND FROM SOUTHERN FLORIDA...  
JUST TO THE NORTH OF THE YUCATAN PENINSULA...INTO CENTRAL  
VERACRUZ. BY THURSDAY EVENING THE BOUNDARY WILL MEANDER ACROSS THE  
NORTHERN BAHAMAS...NORTHERN CUBA... WHILE THE TAIL OF THE FRONT  
STARTS LOSING DEFINITION OVER THE GULF. THIS WILL ALSO CONTINUE  
LEADING TO A TEHUANTEPECER JET. THE JET IS FORECAST TO REACH PEAK  
INTENSITY BETWEEN TUESDAY NIGHT AND EARLY THURSDAY MORNING...WHEN  
IT IS FORECAST TO REACH 50-55KT. A SHEAR LINE IS ALSO ORGANIZING.  
BY TUESDAY EVENING IT WILL EXTEND ACROSS EXTREME WESTERN CUBA INTO  
QUINTANA ROO-NORTHERN GUATEMALA. BY WEDNESDAY EVENING IT WILL  
EXTEND ACROSS THE NORTHERN BAHAMAS...CENTRAL-NORTHERN  
CUBA...BELIZE. BY THURSDAY EVENING THE SHEAR LINE WILL EXTEND  
ACROSS EASTERN HISPANIOLA INTO NORTHEASTERN NICARAGUA.  
 
THE BULK OF PRECIPITATION WITH THE FRONT/SHEAR LINE SYSTEM WILL  
OCCUR ALONG THE GULF OF CAMPECHE AND EASTERN SLOPES OF SOUTHERN  
MEXICO...GUATEMALA...TO EXTEND INTO SOUTHERN BELIZE. BY  
TUESDAY-EARLY WEDNESDAY...EXPECTING THE DEVELOPMENT OF  
THUNDERSTORMS IN SOUTHEASTERN VERACRUZ/TABASCO/NORTHERN CHIAPAS TO  
PRODUCE 10-15MM/DAY AND MAXIMA OF 20-45MM. THIS WILL INCREASE TO  
15-20MM/DAY AND MAXIMA OF 35-70MM ON  
WEDNESDAY-THURSDAY...DECREASING TO 15-20MM/DAY AND MAXIMA OF  
25-50MM ON THURSDAY-FRIDAY. OTHER REGION OF CONTINUED MODERATE  
RAINFALL WILL BE SOUTHERN BELIZE/CENTRAL GUATEMALA. ON  
TUESDAY-WEDNESDAY EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM.  
THIS WILL INCREASE TO 15-20MM/DAY AND MAXIMA OF 25-50MM ON  
WEDNESDAY-THURSDAY EXPANDING INTO MOST OF BELIZE...IN ASSOCIATION  
WITH THE SHEAR LINE. BY THURSDAY-FRIDAY EXPECTING SCATTERED  
CONVECTION FROM NORTHERN HONDURAS INTO BELIZE/CENTRAL GUATEMALA  
WITH ACCUMULATIONS OF 10-15MM/DAY AND MAXIMA OF 20-40MM. INLAND IN  
THE YUCATAN PENINSULA...DIURNAL ACCUMULATIONS WILL GRADUALLY  
INCREASE FROM 00-05MM/DAY AND MAXIMA OF 10MM ON  
TUESDAY-WEDNESDAY...TO 05-10MM/DAY AND ISOLATED MAXIMA OF 15-20MM  
BY THURSDAY-FRIDAY. AS THE FRONT APPROACHES CUBA AND THE  
BAHAMAS...CONVECTION WILL BE SUPPORTED BY THE UPPER LEVELS. THIS  
WILL LEAD TO ACCUMULATIONS OF 05-10MM/DAY AND ISOLATED MAXIMA OF  
15-20MM IN THUNDERSTORMS ON WEDNESDAY THROUGH FRIDAY.  
 
IN THE CENTRAL AND EASTERN CARIBBEAN...SEASONALLY DRY CONDITIONS  
CONTINUE ESTABLISHING. A MID-LEVEL RIDGE WILL BE PRESENT THROUGH  
THE FORECAST CYCLE TO CONTINUE SUSTAINING THE SUBSIDENCE CAP. THE  
RIDGE IS FORECAST TO MEANDER FROM CENTRAL/EASTERN CUBA EAST TO 55W  
ACROSS THE GREATER ANTILLES...AND INTO THE SOUTHEASTERN  
CARIBBEAN/WINDWARD ISLANDS/NORTHEASTERN VENEZUELA. ACTIVITY WILL  
CONCENTRATE IN POCKETS OF ENHANCED TRADE WIND SHOWERS...TO PRODUCE  
LIGHT ACCUMULATIONS. AT LOW-LEVELS...THE REMNANTS OF A SURFACE  
FRONT LIE IN THE TROPICAL ATLANTIC TO THE NORTH OF PUERTO RICO AND  
THE LEEWARD ISLANDS. THE REMNANTS ARE RETROGRESSING WESTWARD IN  
THE FORM OF WEAK WAVES IN THE TRADES. SINCE PRECIPITABLE WATER  
WILL REMAIN LIMITED TO BELOW 40MM AND THE SUBSIDENCE CAP WILL BE  
IN PLACE...EXPECTING LIGHT ACCUMULATIONS. ISOLATED HIGHER AMOUNTS  
ARE EXPECTED IN NORTHEASTERN HISPANIOLA FROM WEDNESDAY THROUGH  
FRIDAY...WHERE A PREFRONTAL THROUGH AND THEN THE SHEAR LINE WILL  
LEAD TO 05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
AS THE MID-LEVEL RIDGE PATTERN DOMINATES THE CARIBBEAN...A  
MID-LEVEL TROUGH IS FORECAST TO PERSIST ACROSS CENTRAL AND  
SOUTHERN CENTRAL AMERICA. THIS WILL CONTINUE STIMULATING THE  
DEVELOPMENT OF CONVECTION ALONG THE CARIBBEAN BASIN OF CENTRAL  
AMERICA. LARGEST ACCUMULATIONS ARE EXPECTED IN COSTA  
RICA/SOUTHEASTERN NICARAGUA/EXTREME WESTERN PANAMA...WHERE  
OROGRAPHIC UPLIFT IN THE SOUTHERN TIER OF THE CARIBBEAN LOW-LEVEL  
JET WILL STIMULATE DEVELOPMENT. THIS WILL SUSTAIN 15-20MM/DAY AND  
MAXIMA OF 25-50MM THROUGH THURSDAY...DECREASING AFTER. IN NORTHERN  
NICARAGUA/EASTERN HONDURAS...EXPECTING A GRADUAL INCREASE TO  
10-15MM/DAY AND MAXIMA OF 20-45MM BY THURSDAY-FRIDAY.  
 
IN NORTHERN SOUTH AMERICA...LARGEST ACCUMULATIONS WILL CLUSTER IN  
COLOMBIA WHILE THE PACIFIC ITCZ REMAINS TO THE NORTH OF ITS  
CLIMATOLOGICAL POSITION. THIS WILL LEAD TO 05-10MM/DAY AND MAXIMA  
OF 15-20MM THROUGH THE CYCLE IN WESTERN COLOMBIA.  
OTHERWISE...EXPECTING DIURNAL CONVECTION TO CONSTRAIN TO THE  
SOUTHERN AMAZON...AND ISOLATED AND LIGHT DIURNAL SHOWERS IN PARTS  
OF THE ANDES. WHILE THE ATLANTIC ITCZ REMAINS IN NORTHERN  
BRAZIL...EXPECTING LIGHT ACCUMULATIONS IN THE GUIANAS THROUGH THE  
CYCLE.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
51W 56W 61W 65W 69W 73W 77W 82W TUTT INDCD  
18N  
67W 72W 76W 80W 84W 88W 92W DISSIPATED EW24N  
 
A TUTT-INDUCED WAVE IS INITIALIZED AT 51W. THIS WAVE WILL ENHANCE  
ACTIVITY IN THE LESSER ANTILLES ON WEDNESDAY MORNING...TO PRODUCE  
05-10MM/DAY AND MAXIMA OF 15MM. ELSEWHERE...THE EFFECTS OF THIS  
WAVE WILL BE LIMITED UNDER THE PRESENCE OF DRY MID-LEVELS.  
 
AN EASTERLY WAVE IS ANALYZED OVER AT 67W. THIS WAVE WILL LEAD TO A  
MINOR ENHANCEMENT IN ACCUMULATIONS IN THE NORTHEASTERN DOMINICAN  
REPUBLIC ON TUESDAY-WEDNESDAY...CAYMAN ISLANDS ON  
WEDNESDAY-THURSDAY...AND THE EASTERN YUCATAN PENINSULA ON FRIDAY.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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