653  
FXCA20 KWBC 161822  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
222 PM EDT FRI APR 16 2021  
 
TROPICAL DISCUSSION FROM APR 16/18 UTC: WEST OVER THE DOMAIN...THE  
MID/UPPER LEVEL FLOW SPLITS BETWEEN A RIDGE EXTENDING OVER THE  
NORTHERN STATES OF MEXICO/SOUTHWEST USA AND A TUTT TO THE  
SOUTH...WITH THE LATTER CENTERING ON A CLOSED LOW TO THE SOUTH OF  
COLIMA/NAYARIT IN SOUTHWEST MEXICO. THROUGH SATURDAY THE RIDGE IS  
TO COLLAPSE AS POLAR TROUGH AMPLIFIES ACROSS THE WESTERN USA TO  
THE NORTHERN STATES OF MEXICO. THE TUTT TO THE SOUTH IS TO THEN  
LIFT ACROSS CENTRAL/SOUTHERN MEXICO WHILE SLOWLY PHASING WITH THE  
POLAR TROUGH TO THE NORTH. AT LOW LEVELS...AN ELONGATED FRONT IS  
TO STRETCH ACROSS THE SOUTHERN USA EARLY IN THE CYCLE. ON SATURDAY  
THIS SURGES ACROSS TEXAS/THE RIO BRAVO TO THE NORTHEAST STATES OF  
MEXICO WHILE TRIGGERING A PREFRONTAL SHEAR LINE ACROSS VERACRUZ  
AND INDUCING A PREFRONTAL TROUGH OVER THE YUCATAN. ON SUNDAY THE  
FRONT MOVES FARTHER SOUTH ACROSS TAMAULIPAS TO VERACRUZ...WITH THE  
PREFRONTAL TROUGH PERSISTING OVER GUATEMALA/THE YUCATAN WHILE THE  
SHEAR LINE BECOMES ILL DEFINED. INITIALLY...LIGHT DIURNAL  
CONVECTION IS TO CLUSTER ALONG THE SIERRA MADRE ORIENTAL INTO  
CENTRAL MEXICO...WITH RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA  
OF 10MM IN AFTERNOON CONVECTION. AS THE FRONT SURGES ACROSS  
TAMAULIPAS-COAHUILA ON SATURDAY ACTIVITY INCREASES TO 05-10MM/DAY  
AND MAXIMA OF 15-30MM...WHILE OVER VERACRUZ THE PREFRONTAL SHEAR  
LINE IS TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
30-60MM. ON SUNDAY THIS WEAKENS TO 05-10MM/DAY AND MAXIMA OF 15MM  
WHILE BUILDING SOUTH ACROSS CENTRAL MEXICO. ACTIVITY WITH THE  
PREFRONTAL SHEAR LINE OVER THE YUCATAN-TABASCO IS TO LINGER  
THROUGH THE WEEKEND...INCREASING FROM 00-05MM/DAY AND MAXIMA OF  
10MM ON SATURDAY TO 10-15MM/DAY AND MAXIMA OF 20-30MM ON SUNDAY AS  
ENHANCED BY THE REMNANTS OF THE UPPER LEVEL TUTT. THIS IS TO ALSO  
FAVOR AN INCREASE ACROSS SOUTHERN GUATEMALA-SOUTHERN HONDURAS/EL  
SALVADOR...WITH ACTIVITY INCREASING FROM 05-10MM/DAY AND MAXIMA OF  
15MM ON SATURDAY TO 15-20MM/DAY AND MAXIMA OF 25-50MM ON SUNDAY.  
 
DOWNSTREAM OVER THE WESTERN ATLANTIC...A BROAD/LOW AMPLITUDE  
TROUGH REMAINS THE DOMINANT FEATURE NORTH OF THE ISLANDS. AT MID  
LEVELS...SHORT WAVE PERTURBATIONS ROUNDING THE BASE OF THE TROUGH  
ARE TO STREAM ACROSS THE BAHAMAS-NORTHERN HISPANIOLA/PUERTO RICO  
DURING THROUGH THIS EVENING. AT 250 HPA A 70-90KT JET MAXIMA IS TO  
ACCOMPANY THESE PERTURBATIONS AS THE STREAM TO THE  
NORTH...FAVORING WEAK DIVERGENCE ALOFT AS IT SLOWLY RELOCATES  
NORTH OF THE ISLANDS. AT LOW LEVELS...A SHALLOW FRONT LIFTS ACROSS  
THE NORTHEAST CARIBBEAN TO PUERTO RICO-HISPANIOLA EARLY IN THE  
CYCLE...WITH BOUNDARY FORECAST TO FRONTOLIZE EARLY ON SATURDAY  
MORNING. AS IT LIFTS ACROSS THE NORTHEAST CARIBBEAN PWAT CONTENT  
SURGES TO 35-40MM...THEN RAPIDLY PLUMMETS ON SATURDAY AS A DRYER  
AIR MASS ENTRAINS FROM THE EAST. MEANWHILE...THIS WILL FEED  
AFTERNOON CONVECTION ACROSS THE DOMINICAN REPUBLIC...PUERTO RICO  
AND THE VIRGIN ISLANDS. OVER THE DOMINICAN REPUBLIC EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM...WHILE OVER  
PUERTO RICO EXPECTING ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF  
25-50MM. LESSER AMOUNTS ARE EXPECTED OVER THE NORTHERN LEEWARD AND  
THE VIRGIN ISLES...WITH ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF  
10MM.  
 
DURING THE WEEKEND...ENVIRONMENTAL CONDITIONS ACROSS THE NORTHERN  
CARIBBEAN WILL QUICKLY GROW HOSTILE TO DEVELOPMENT AS MID/UPPER  
LEVEL RIDGE ROLLS FROM THE WEST ACROSS THE BASIN. THE MID LEVEL  
RIDGE SETTLES ON A CLOSED HIGH OVER PUERTO RICO/HISPANIOLA ON  
SUNDAY-EARLY MONDAY MORNING...THEN RELOCATES TO THE CENTRAL  
ATLANTIC. STARTING ON SATURDAY...UNDER THE INFLUENCE OF THIS  
RIDGE...THE TRADE WINDS INVERSION ACROSS THE NORTHEAST CARIBBEAN  
IS TO STRENGTHEN. AT LOW LEVELS THIS WILL COMBINE WITH A DRY AND  
DUSTY SAHARAN AIR LAYER ADVECTING ACROSS THE ISLAND CHAIN TO  
GENERALLY FAVOR FAIR WEATHER CONDITIONS. THIS WILL GRADUALLY  
SPREAD INTO THE GUIANAS AND VENEZUELA DURING THE WEEKEND/EARLY  
NEXT WEEK...WHERE IT IS TO ALSO DAMPEN CONVECTIVE DEVELOPMENT.  
 
MEANWHILE...SOUTHERN CENTRAL AMERICA AND NORTHERN SOUTH AMERICA  
WILL LIE UNDER THE INFLUENCE OF AN UPPER LEVEL CELL OF THE  
SUBEQUATORIAL RIDGE. THIS IS TO EXTEND WEST ACROSS THE  
GUIANAS-VENEZUELA TO COLOMBIA/SOUTHERN CENTRAL AMERICA. THE RIDGE  
ALOFT IS TO VENT DIURNAL CONVECTION. EARLY IN THE CYCLE IT  
COMBINES WITH AN ATMOSPHERIC KELVIN WAVE STREAMING ACROSS THE  
CENTRAL TO THE EASTERN CARIBBEAN TO SUSTAIN THE NORTHWARD  
MODULATION OF THE EASTERN PACIFIC ITCZ INTO PANAMA/COSTA  
RICA-NORTHWEST COLOMBIA. OVER PANAMA-COSTA RICA THIS IS TO  
INITIALLY FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
35-70MM. DURING THE WEEKEND...AS THE KELVIN WAVE PULLS AWAY...THIS  
DECREASES TO 10-15MM/DAY AND MAXIMA OF 20-40MM. ON THE ANDEAN  
REGION OF COLOMBIA INITIALLY EXPECTING RAINFALL AMOUNTS OF  
20-30MM/DAY AND MAXIMA OF 40-80MM...DECREASING TO 15-20MM/DAY AND  
MAXIMA OF 30-60MM ON SATURDAY. ON SUNDAY IT DROPS TO 10-15MM/DAY  
AND MAXIMA OF 20-40MM. LESSER AMOUNTS ARE EXPECTED TO THE NORTH  
ACROSS NORTHERN COLOMBIA TO SANTANDERES/MARACAIBO VENEZUELA...WITH  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM. OVER AMAZONIA  
TO THE SOUTH...EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND  
MAXIMA OF 20-45MM...WITH LOCALLY HIGHER AS ENHANCED BY IRREGULARLY  
SPACED EASTERLY WAVES STREAMING ACROSS BRASIL.  
 
TROPICAL WAVES/TUTT INDUCED PERTURBATIONS/TRADE WIND SURGES  
NONE SIGNIFICANT  
 
DAVISON...WPC (USA)  

 
 
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