901  
FXCA20 KWBC 231821  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
220 PM EDT THU MAR 23 2017  
 
TROPICAL DISCUSSION FROM MARCH 23/12 UTC: CONSISTENT WITH PREVIOUS  
FORECASTS...A MID/UPPER LEVEL TROUGH IS TO PULL ACROSS THE  
SOUTHWEST USA...MOVING ACROSS OKLAHOMA/TEXAS ON FRIDAY  
EVENING...AND TO THE MISSISSIPPI BASIN ON SATURDAY. THE TROUGH IS  
TO PRESS AGAINST A RIDGE TO THE EAST AND SOUTH. UNDER PRESSURE THE  
RIDGE OVER MEXICO IS TO GRADUALLY WEAKEN/NEARLY COLLAPSE ON  
FRIDAY. AS THE RIDGE WEAKENS IT IS TO FAVOR GRADUAL EROSION OF MID  
LEVEL CAP INVERSION OVER MEXICO...WITH DEEPER INSTABILITY ON THE  
SOUTHWEST STATES OF MEXICO ON FRIDAY TO SATURDAY TO FAVOR AN  
INCREASE IN DIURNAL CONVECTION. EARLY IN THE CYCLE EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. THROUGH  
SATURDAY THIS WILL INCREASE TO 10-15MM/DAY AND MAXIMA OF 20-30MM.  
AT LOW LEVELS...THE ASSOCIATED FRONT IS TO CONFINE TO THE  
SOUTHWEST USA/EXTREME NORTHERN PORTIONS OF MEXICO EARLY IN THE  
CYCLE...WITH CONVECTION LIMITING TO NORTH OF THE BORDER.  
 
A MID LEVEL RIDGE OVER THE EASTERN USA FAVORS THE SOUTHWARD  
AMPLIFICATION OF A LONG WAVE TROUGH ACROSS THE WESTERN ATLANTIC TO  
THE NORTHWEST CARIBBEAN...WHERE IT IS TO PHASE WITH A SHORT WAVE  
TROUGH TO THE SOUTH. AS THE MID LEVEL RIDGE ENCROACHES INTO THE  
WESTERN ATLANTIC ON FRIDAY-SATURDAY...IT IS TO UNDERCUT THE TROUGH  
TO THE EAST. THIS IS TO THEN EVOLVE INTO A MID LEVEL LOW OVER THE  
BAHAMAS WHILE A SHORT WAVE TROUGH REMAINS OVER THE  
CENTRAL/SOUTHERN CARIBBEAN TO SOUTHERN CENTRAL AMERICA. EARLY IN  
THE CYCLE THE AMPLIFYING TROUGH WILL PRESS AGAINST A CELL OF THE  
SUBEQUATORIAL RIDGE TO THE SOUTH AND EAST. THIS IS TO TIGHTEN THE  
GRADIENT WHILE FAVORING INTENSIFICATION OF A SUBTROPICAL JET  
MAXIMA ROUNDING THE BASE OF THE LONG WAVE TROUGH. THE JET MAXIMA  
IS TO SLOWLY LIFT ACROSS THE CENTRAL CARIBBEAN-HISPANIOLA.  
DIVERGENCE ON ITS RIGHT ENTRANCE REGION IS TO VENT DEEP CONVECTION  
ACROSS SOUTHERN CENTRAL AMERICA-COLOMBIA/NORTHWEST VENEZUELA EARLY  
IN THE CYCLE...AND ACROSS HISPANIOLA-PUERTO RICO/VIRGIN ISLES ON  
FRIDAY THROUGH SUNDAY. AS THE SUBEQUATORIAL RIDGE YIELDS TO THE  
POLAR TROUGH...TRADE WINDS CAP OVER THE NORTHEAST CARIBBEAN IS TO  
GRADUALLY WEAKEN THROUGH FRIDAY. THIS...IN-TURN...WILL FAVOR  
DEEPER LAYER CONVECTIVE INSTABILITY OVER THE NORTHEAST CARIBBEAN  
ISLES DURING THE NEXT FEW DAYS.  
 
AT LOW LEVELS...BROAD RIDGE OVER THE EASTERN USA IS DRIVING A  
POLAR FRONT SOUTH ACROSS THE WESTERN ATLANTIC TO THE NORTHWEST  
BAHAMAS. THROUGH FRIDAY MORNING THE FRONT WILL MEANDER SOUTH TO  
THE CENTRAL BAHAMAS...AND LATER IN THE DAY IT IS TO BOTTOM OUT  
ALONG 22N/23N WHILE MEANDERING OVER THE BAHAMAS TO THE FLORIDA  
PENINSULA. AS IT ENTERS THE NORTHWEST BAHAMAS THE FRONT WILL  
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM  
THROUGH FRIDAY MORNING...WHILE OVER THE CENTRAL/SOUTHEAST BAHAMAS  
AND THE TURKS IT IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15MM ON FRIDAY-SATURDAY. ALSO...THE SURGING FRONT IS TO  
SUSTAIN A PREFRONTAL SHEAR LINE ACROSS HISPANIOLA-CENTRAL  
CARIBBEAN EARLY IN THE CYCLE...WHERE IT IS TO MEANDER DURING THE  
NEXT 48-54 HRS. THE SHEAR LINE WILL FAVOR STRONG BOUNDARY LAYER  
WINDS OF 20-25KT ACROSS HISPANIOLA-JAMAICA. THE STRONG WINDS WILL  
FAVOR TOPOGRAPHICALLY INDUCED CONVECTION ACROSS  
HISPANIOLA...TRIGGERING RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA  
OF 30-60MM THROUGH FRIDAY MORNING. ON FRIDAY TO SATURDAY...UNDER  
FAVORABLE JET DYNAMICS...THIS WILL INCREASE TO 30-60MM/DAY AND  
MAXIMA OF 75-125MM. OVER JAMAICA...INITIALLY EXPECTING RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON FRIDAY...AS THE  
WINDS SURGE ACROSS THE WINDWARD CHANNEL/HAITIAN PENINSULA...AND  
WITH DEW POINT TEMPERATURES OF 18-19C...THIS WILL INCREASE TO  
15-20MM/DAY AND MAXIMA OF 25-50MM...WITH MOST INTENSE ON THE  
NORTHEAST PARISHES.  
 
THE DEEP POLAR TROUGH OVER THE WESTERN ATLANTIC ALSO FAVORS AN  
INDUCED/PREFRONTAL TROUGH ACROSS THE CENTRAL CARIBBEAN/HISPANIOLA.  
THIS...IN COMBINATION WITH BROAD RIDGE OVER THE CENTRAL/EASTERN  
ATLANTIC FAVORS A MOIST SOUTHEASTERLY FLOW ACROSS THE ISLAND CHAIN  
TO PUERTO RICO/VIRGIN ISLES. THROUGH FRIDAY THIS IS TO FAVOR AN  
INCREASE IN MOISTURE CONTENT...WITH PWAT EXPECTED TO PEAK AROUND  
50MM. THIS WILL COMBINE WITH UPPER TROUGH PATTERN/FAVORABLE JET  
DYNAMICS TO SUSTAIN AN INCREASE IN CONVECTION. EARLY IN THE CYCLE  
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-45MM.  
ON FRIDAY THIS INCREASES TO 20-30MM/DAY AND MAXIMA OF  
50-100MM...WHILE ON SATURDAY IT DECREASES TO 15-20MM/DAY AND  
MAXIMA OF 35-70MM. OTHER CONVECTION IS EXPECTED OVER THE  
LEEWARD/VIRGIN ISLES...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-25MM ON FRIDAY...AND 00-05MM/DAY AND MAXIMA OF 10MM  
ON SATURDAY. LATER DURING THE WEEKEND...UNDER THE INFLUENCE OF THE  
MID LEVEL CYCLONE OVER THE BAHAMAS...THE INDUCED TROUGH IS TO  
EVOLVE INTO A CLOSED LOW JUST NORTH OF HISPANIOLA/EAST OF THE  
TURKS AND CAICOS. NOTE THAT SOME OF THE MODELS SUGGEST POSSIBILITY  
OF SUBTROPICAL CYCLONE FORMING AS THE LOW LEVEL CIRCULATION  
EVOLVES INTO A WARM CORE SYSTEM. THE LOW WILL BECOME FOCUS OF LOW  
LEVEL MOISTURE CONVERGENCE...WITH ORGANIZED DEEP CONVECTION TO  
CLUSTER ALONG THIS FEATURE. ACROSS HISPANIOLA AND THE TURKS THIS  
IS TO THEN FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
25-50MM. OVER THE SOUTHERN CARIBBEAN...UNDER FAVORABLE JET  
DYNAMICS EARLY IN THE CYCLE....EXPECTING CONVECTION ON THE  
CARIBBEAN COASTAL PLAINS OF COSTA RICA-BOCAS DEL TORO IN WESTERN  
PANAMA TO INCREASE TO 15-20MM/DAY AND MAXIMA OF 25-50MM DURING THE  
DAY TODAY. ON FRIDAY-SATURDAY THIS DECREASES TO 10-15MM/DAY AND  
MAXIMA OF 20-35MM. THIS IS TO ALSO INDUCE A SURGE IN CONVECTION  
ACROSS NORTHERN COLOMBIA AND VENEZUELA...WITH MOST ACTIVE OVER  
COLOMBIA TO CLUSTER BETWEEN THE EJE CAFETERO AND THE SIERRA NEVADA  
DE SANTA MARTA...WHILE OVER VENEZUELA EXPECTING MOST INTENSE TO  
THE NORTHWEST...WITH RAINFALL AMOUNTS OF 30-40MM/DAY AND MAXIMA OF  
75-125MM. AS THE JET PULLS ON FRIDAY THIS DECREASES TO 15-30MM/DAY  
AND MAXIMA OF 40-80MM...WHILE ON SATURDAY EXPECTING RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. THIS IS TO ALSO  
ENHANCE CONVECTION ACROSS THE ABC ISLES/NORTH COAST OF  
VENEZUELA...TO RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM. THROUGH SATURDAY MAXIMA DECREASES TO 15MM/DAY  
IN SCATTERED CONVECTION.  
 
THE SUBEQUATORIAL RIDGE TO THE SOUTH EXTENDS WEST ACROSS THE  
TROPICAL ATLANTIC TO NORTHERN SOUTH AMERICA. THE RIDGE IS TO HOLD  
DURING THE NEXT FEW DAYS. ACROSS THE GUIANAS DIURNAL  
CONVECTION/SEA BREEZE CONVERGENCE IS TO FAVOR RAINFALL AMOUNTS OF  
00-05/DAY AND WIDELY ISOLATED MAXIMA OF 10MM/DAY THROUGH SUNDAY  
MORNING. HIGHER AMOUNTS ARE EXPECTED OVER AMAZONIA IN SOUTHERN  
VENEZUELA AND COLOMBIA...WHERE DIURNAL/NEAR EQUATORIAL TROUGH  
RELATED CONVECTION IS TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM/DAY  
AND MAXIMA OF 25-50MM IN SCATTERED CONVECTION.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
17W 20W 23W 26W 30W 32W 36W 40W TW  
27W 31W 35W 38W 40W 42W 44W 47W TW  
 
TROPICAL WAVE ALONG 17W AND 27W WILL CONFINE TO THE ATLANTIC ITCZ  
DURING THE NEXT FEW DAYS.  
 
JIMENEZ...IMN (COSTA RICA)  
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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