622  
FXCA20 KWBC 301927  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
227 PM EST THU NOV 30 2017  
 
TROPICAL DISCUSSION FROM NOV 30/12 UTC: A 500 HPA HIGH OVER  
CENTRAL MEXICO ANCHORS A RIDGE THAT EXTENDS OVER MEXICO-TEXAS TO  
THE GULF OF MEXICO. THE RIDGE IS TO SLOWLY BUILD EAST ACROSS THE  
YUCATAN PENINSULA TO THE WESTERN CARIBBEAN ON FRIDAY...TO HOLD  
THROUGHOUT THE WEEKEND. THE PERSISTENT MID LEVEL RIDGE IS STEERING  
SHORT WAVE PERTURBATIONS ACROSS THE EASTERN USA TO THE WESTERN  
ATLANTIC. IN THIS PATTERN...A SHORT WAVE TROUGH MOVES NORTH OF THE  
GREATER ANTILLES LATER TODAY AS A SECONDARY VORTEX STREAMS ACROSS  
THE BAHAMAS LATER ON FRIDAY. THESE PERTURBATIONS ARE TO GRADUALLY  
COMBINE IN SUPPORT OF A BROAD TROUGH OVER THE WESTERN  
ATLANTIC-NORTHERN CARIBBEAN ISLES. AS THE TROUGH DEEPENS ACROSS  
THE WESTERN ATLANTIC IT IS TO PRESS AGAINST A CELL OF THE  
SUBEQUATORIAL RIDGE MEANDERING OVER THE EASTERN CARIBBEAN. UNDER  
PRESSURE THE RIDGE TENDS TO WEAKEN EARLY DURING THE WEEKEND. EARLY  
IN THE PERIOD THIS SUSTAINS A STRONG TRADE WINDS CAP ACROSS THE  
NORTHEAST CARIBBEAN ISLES. BUT AS THE RIDGE WEAKENS...THE  
INVERSION IS FORECAST TO GRADUALLY LIFT. THIS WILL THEN ALLOW FOR  
DEEPER MOISTURE TO POOL ACROSS THE EASTERN CARIBBEAN. AT 250 HPA A  
SUBTROPICAL JET MAXIMA IS TO ROUND THE BASE OF THE TROUGH. AS THE  
GRADIENT TIGHTENS DURING THE WEEKEND...THE JET MAXIMA IS FORECAST  
TO INTENSIFY LATER ON SUNDAY-MONDAY. THIS IS TO THEN FAVOR AN  
UPPER DIVERGENT PATTERN ACROSS THE NORTHEAST CARIBBEAN ISLES.  
 
AT LOW LEVELS THE MID LEVEL VORTICES ARE TO INTERACT WITH  
MEANDERING FRONT THAT EXTENDS NORTH OF THE ISLANDS. THE FIRST  
PERTURBATION INDUCED A FRONTAL LOW THAT IS TO GRADUALLY DEEPEN AS  
IT MEANDERS EAST...WITH THE SURFACE LOW CENTERING BETWEEN PUERTO  
RICO AND BERMUDA LATER THIS AFTERNOON. AS THE LOW LEVEL CYCLONE  
BECOMES BETTER ORGANIZED...IT IS TO DRIVE A SURFACE FRONT SOUTH  
ACROSS THE BAHAMAS TO CENTRAL/WESTERN CUBA EARLY ON FRIDAY  
MORNING. SIMULTANEOUSLY...A LOW LEVEL RIDGE IS TO SLOWLY BUILD  
ACROSS THE GULF OF MEXICO-SOUTHEAST USA ON FRIDAY-SATURDAY. AS THE  
RIDGE BUILDS IT IS TO SUSTAIN A BRISK NORTHEASTERLY FLOW ACROSS  
CUBA-THE BAHAMAS TO THE WESTERN CARIBBEAN...WITH BOUNDARY LAYER  
WINDS OVER THE BAHAMAS-CUBA TO PEAK AT 15-20KT. OVER THE WESTERN  
CARIBBEAN/NORTHERN CENTRAL AMERICA THE WINDS ARE TO PEAK AT  
20-25KT. AS THE WINDS INTENSIFY THE FRONT IS TO MOVE SOUTH ACROSS  
THE TURKS AND CAICOS WHILE TRAILING ACROSS CUBA EARLY ON SATURDAY  
MORNING. ON SUNDAY MORNING IT MOVES TO NORTHERN HISPANIOLA.  
FURTHERMORE...THE DEEPENING SURFACE LOW IS TO INDUCE AN INVERTED  
TROUGH ACROSS THE EASTERN CARIBBEAN EARLY IN THE CYCLE. THIS IS TO  
ENHANCE MOISTURE TRANSPORT ACROSS THE WINDWARD ISLES TO THE  
EASTERN CARIBBEAN. ALSO...THE SURGING FRONT WILL SUSTAIN A  
PREFRONTAL SHEAR LINE ACROSS PUERTO RICO TO THE CENTRAL CARIBBEAN  
LATER ON FRIDAY. DURING THE DAY ON SATURDAY THIS IS TO MEANDER  
ACROSS PUERTO RICO-VIRGIN ISLES...REACHING THE NORTHERN LEEWARD  
ISLES EARLY ON SUNDAY MORNING.  
 
ACROSS THE BAHAMAS-CUBA THE FRONT AND COLD POST FRONTAL  
NORTHERLIES ARE TO FAVOR SCATTERED CONVECTION. OVER THE BAHAMAS  
THIS IS TO SUSTAIN RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF  
10MM/DAY. ON SUNDAY...FOCUS OF THE CONVECTION SHIFTS TO THE  
SOUTHEAST BAHAMAS AND THE TURKS...WITH RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM. ACROSS CUBA INITIALLY EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ON FRIDAY AND  
SATURDAY THIS IS TO THEN RESULT IN ACCUMULATION OF 00-05MM/DAY AND  
MAXIMA OF 10MM/DAY...WHILE ON SUNDAY THE MAXIMA ACROSS EASTERN  
CUBA IS TO PEAK AT 15-25MM. ACROSS NORTHERN HISPANIOLA EXPECTING  
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM ON THURSDAY TO  
SATURDAY... WHILE ON SUNDAY EXPECTING ACCUMULATION OF 05-10MM/DAY  
AND MAXIMA OF 15MM. OVER PUERTO RICO-VIRGIN ISLES THE PREFRONTAL  
SHEAR LINE IS TO TRIGGER RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM LATER ON FRIDAY AND DURING THE DAY ON SATURDAY...  
WHILE ON SUNDAY-MONDAY THE FRONT IS TO FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM. OVER THE LEEWARD ISLES THE  
PREFRONTAL SHEAR LINE IS TO THEN FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM EARLY ON SUNDAY MORNING...WHILE  
ON SUNDAY-MONDAY IT DECREASES TO 00-05MM/DAY AND MAXIMA OF 10MM.  
 
OVER THE EASTERN CARIBBEAN...THE INDUCED PREFRONTAL TROUGH IS TO  
SUSTAIN A MOIST SOUTHEASTERLY FLOW ACROSS THE WINDWARD ISLANDS. AS  
MOISTURE SURGES ACROSS THE EASTERN CARIBBEAN IT IS TO SUSTAIN  
SCATTERED CONVECTION OVER TRINIDAD/TOBAGO-THE WINDWARD ISLES. OVER  
TRINIDAD-TOBAGO AND THE GRENADINES EXPECTING ACCUMULATION OF  
10-15MM/DAY AND MAXIMA OF 20-40MM. THROUGH SATURDAY THIS DECREASES  
TO 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER WINDWARD-SOUTHERN  
FRENCH ISLES THIS WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY  
AND MAXIMA OF 15-20MM/DAY THROUGH SATURDAY MORNING.  
 
OVER THE WESTERN CARIBBEAN...THE BRISK NORTHEASTERLY WINDS ARE TO  
ENHANCE MOISTURE CONVERGENCE ACROSS NORTHERN HONDURAS-SOUTHERN  
BELIZE. EARLY IN THE PERIOD EXPECTING RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-30MM. ON FRIDAY-SATURDAY FOCUS OF THE  
CONVECTION SHIFTS TO NORTHWEST HONDURAS-SOUTHERN BELIZE...WITH  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM...WHILE OVER  
NORTHEAST HONDURAS/NICARAGUA EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM. ON SUNDAY-MONDAY THIS INCREASES  
TO 10-15MM/DAY AND MAXIMA OF 20-30MM. OVER THE CAYMAN ISLES THIS  
IS TO FAVOR LIGHT RAINFALL AMOUNTS WITH ACCUMULATION OF  
05-10MM/DAY AND MAXIMA OF 15MM EARLY IN THE CYCLE...WHILE ACROSS  
JAMAICA EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF  
10MM ON FRIDAY. ON SUNDAY THIS INCREASES TO 05-10MM/DAY AND MAXIMA  
OF 15MM.  
 
AS THE TRADES OVER THE WESTERN CARIBBEAN/CENTRAL AMERICA  
INTENSIFY...THIS IS TO SLOWLY DRIVE THE EASTERN PACIFIC ITCZ  
SOUTH. ACROSS SOUTHERN NICARAGUA-COSTA RICA TO PANAMA EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER EJE  
CAFETERO IN NORTHWEST COLOMBIA...INITIALLY EXPECTING RAINFALL  
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM. BUT AS THE ITCZ  
MEANDERS SOUTH THIS GRADUALLY DECREASES TO 05-10MM/DAY AND MAXIMA  
OF 15-25MM ON SATURDAY-SUNDAY. LIKEWISE...OVER THE CAUCA VALLEY TO  
THE SOUTHWEST...INITIALLY EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM. ON SATURDAY-SUNDAY THIS INCREASES  
TO 15-20MM/DAY AND MAXIMA OF 25-50MM. ON THE ANDEAN REGION OF  
COLOMBIA-SOUTHERN VENEZUELA EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM/DAY.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
38W 41W 44W 47W 49W 52W 55W 58W TWS  
11N  
63W 65W 67W 69W 70W 72W 74W 76W EW  
14N  
 
A TRADE WIND SURGE IS INITIALIZED ALONG 38W AND SOUTH OF  
11N...WITH A DRY SAHARAN AIR LAYER TRAILING THIS PERTURBATION.  
THIS REACHES FRENCH GUIANA EARLY ON SATURDAY MORNING TO FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. THIS  
SPREADS ACROSS SURINAME LATER IN THE DAY/EARLY SUNDAY MORNING.  
ACROSS NORTHERN GUYANA-NORTHEAST VENEZUELA THIS IS TO THEN TRIGGER  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM ON SUNDAY TO  
MONDAY.  
 
AN EASTERLY WAVE ALONG 63W AND TO THE SOUTH OF 14N IS TO ENHANCE  
DIURNAL CONVECTION ACROSS SOUTHERN VENEZUELA AND COLOMBIA TO FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. ACROSS THE  
ABC ISLANDS EXPECTING SIMILAR RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM/DAY ON FRIDAY AND SATURDAY.  
 
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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