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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1055Z May 21, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
655 AM EDT MON MAY 21 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 21/06
UTC: AT MID/UPPER LEVELS...A HIGH NEAR 30N 70W ANCHORS A RIDGE
OVER THE WESTERN ATLANTIC. A TUTT LIES TO THE EAST-SOUTHEAST OF
THIS RIDGE...WITH AXIS CENTERING ON A MID LEVEL CLOSED LOW NEAR
23N 56W. THIS LOW EXTENDS A TROUGH TO THE NORTHEAST CARIBBEAN...
WHERE IT FAVORS AN UPPER CONVERGENT PATTERN AND AN ELEVATED TRADE
WINDS CAP. PER SATELLITE DERIVED PWAT ANALYSIS...DEEPER MOISTURE
IS POOLING CLOSER TO THE TUTT LOW...WHILE A DRYER AIR MASS
ENVELOPS THE NORTHEAST CARIBBEAN ISLES. AT LOW LEVELS...BROAD
RIDGE OVER THE CENTRAL ATLANTIC FAVORS BRISK EASTERLY TRADES
ACROSS THE FORECAST AREA. THIS WILL CONTRIBUTE TO GENERATION OF
STREAMERS LATER THIS MORNING.

MID/UPPER LEVEL RIDGE IS TO DRIFT SOUTH AS THE WEEK WEARS
ON...SETTLING OVER THE EASTERN CARIBBEAN LATER IN THE WEEK. THE
TUTT...MEANWHILE...IS TO REMAIN TO THE EAST-NORTHEAST OF THE
LEEWARD ISLES DURING THE NEXT FEW DAYS...WITH PATTERN TO UNRAVEL
LATER IN THE WEEK AS THE RIDGE STRENGTHENS ITS FOOTHOLD OVER THE
EASTERN CARIBBEAN AND THE TUTT WEAKENS. MEANWHILE...THE MEANDERING
TUTT IS TO CONTINUE TO FAVOR AN UPPER CONVERGENT PATTERN THAT IS
TO INHIBIT DEEP CONVECTION...WITH SHALLOW CONVECTION CAPPING
AROUND 650-700 HPA. THIS IS HIGH ENOUGH TO ALLOW MOIST PLUME TO
THE EAST OF THE LEEWARD ISLES TO GRADUALLY ADVECT ACROSS THE
NORTHEAST CARIBBEAN ON WEDNESDAY-THURSDAY. DURING THAT PERIOD PWAT
CONTENT WILL INCREASE FROM 15-20MM TO AROUND 30-35MM. THIS WILL BE
HIGH ENOUGH TO SUSTAIN AN INCREASE IN DIURNAL CONVECTION ACROSS
THE FORECAST AREA. AT LOW LEVELS THIS WILL BE ACCOMPANIED BY A
WIND SHIFT...WITH WINDS VEERING TO THE EAST-SOUTHEAST WHILE
DROPPING TO LESS THAN 15KT.

IN EASTERLY TRADES...MOST ACTIVE CONVECTION IS TO CLUSTER ACROSS
EL YUNQUE RAINFOREST AND WESTERN PORTIONS OF PUERTO RICO...WITH
MODELS AGREEING ON POTENTIAL FOR MODERATE/LOCALLY HEAVY RAINFALL
AMOUNTS DURING THE LATE AFTERNOON HOURS. ON WEDNESDAY AND
ONWARD...AS THE WINDS SHIFT TO THE SOUTHWEST...FOCUS OF THE
HEAVIER CONVECTION WILL SHIFT TO NORTHWEST PUERTO RICO. THE SHORT
RANGE PATTERN IS WELL DEPICTED BY THE NAM AND THE NMM VERSION OF
THE HRWRF. CONFIDENCE IN THE FORECAST IS HIGH.

DAVISON...WPC (USA)