Prognostic Meteorological Discussion
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FXCA20 KWBC 171047
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
646 AM EDT THU AUG 17 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM AUG 17/06
UTC. DEEP TUTT LOW OVER THE SOUTHEAST BAHAMAS EXTENDS A SHORT WAVE
TROUGH TO THE CENTRAL CARIBBEAN. THIS FAVORS AN UPPER DIVERGENT
PATTERN ACROSS HISPANIOLA-PUERTO RICO-NORTHERN LEEWARD ISLES THAT
IS VENTING DEEP CONVECTION IN ASSOCIATION WITH A TUTT INDUCED
TROUGH/EASTERLY WAVE IN THE LOW LEVEL TRADES. FAVORABLE
ENVIRONMENTAL CONDITIONS ARE TO GENERALLY PERSIST DURING MOST OF
THE DAY TODAY...WITH MOST INTENSE CONVECTION CLUSTERING OVER THE
VIRGIN ISLES/EASTERN PUERTO RICO-SAN JUAN METRO AREA DURING THE
MORNING HOURS. SAN JUAN RADAR SHOWS CONVECTIVE CELLS TRAINING
ACROSS FARJARDO/LUQUILLO-CAROLINA AND PORTIONS OF THE SAN JUAN
METRO AREA. THIS IS LIKELY TO RESULT IN RAINFALL AMOUNTS OF 3-4
INCHES...WITH LOCALIZED MAXIMA OF 6-8 INCHES HIGHLY PROBABLE. ALSO
UNDER INFLUENCE OF THE LOW LEVEL PERTURBATION... LOW/MID LEVEL
WINDS ARE VEERING TO THE SOUTHEAST. THIS IS ENHANCING MOISTURE
CONVERGENCE ACROSS THE CARIBBEAN COAST OF PUERTO RICO...WITH HEAVY
RAINS TO ALSO AFFECT PONCE AND VICINITY. A SECONDARY MAXIMA IS
EXPECTED OVER NORTHWEST PUERTO RICO LATER THIS MORNING/EARLY
AFTERNOON. THE GFS GDI FORECAST DID A GOOD JOB IN HIGHLIGHTING THE
POTENTIAL FOR HEAVY CONVECTION AND ENVIRONMENTAL CONDITIONS
FAVORABLE FOR MCS DEVELOPMENT. BOTH VERSIONS OF THE HRWRF DID A
POOR JOB IN RESOLVING AREAS OF HEAVY RAINFALL...AND LATEST RUN NOT
DOING ANY BETTER.

A MID/UPPER LEVEL RIDGE IS TO THEN BUILD FROM THE NORTH AND
EAST...TO DISPLACE THE TUTT FARTHER TO THE WEST. THIS IS TO THEN
STRENGTHEN THE TRADE WINDS CAP LATER THIS EVENING/EARLY FRIDAY
MORNING...TO SUSTAIN EROSION OF AVAILABLE MOISTURE. THE STRONG CAP
IS TO HOLD THROUGH SATURDAY MORNING...LIFTING ABOVE 600 HPA BY
MIDDAY ON SATURDAY. THE MID LEVEL RIDGE IS STEERING A COUPLE OF
TROPICAL WAVES ACROSS THE TROPICAL ATLANTIC...WITH ONE ALONG 53W
AND THE OTHER NEAR 42W EARLY THIS MORNING. THE FORMER ENTERS THE
WINDWARD ISLES BY MIDDAY ON FRIDAY. THE RIDGE IS TO BLOCK THIS
FEATURE FAR TO THE SOUTH...SO MOST ACTIVE WEATHER IS EXPECTED OVER
OPEN WATERS TO THE SOUTH. THE NEXT ENTER THE LEEWARD ISLES EARLY
ON SUNDAY MORNING...CROSSING THE VIRGIN ISLES TO EASTERN PUERTO
RICO BY DAWN. BEST DYNAMICAL FORCING WITH THIS FEATURE IS TO TAKE
PLACE DURING THE DAYTIME HOURS. IN RESPONSE...GDI FORECAST SHOWS
AN ENHANCED RISK OF THUNDERSTORMS IN ASSOCIATION WITH THIS
FEATURE. LACKING STRONG UPPER LEVEL SUPPORT IT SHOULD NOT BE AS
ACTIVE AS THE ONE TODAY...SO EXPECTING LESSER RAINFALL AMOUNTS.

GUY...NMS (BELIZE)
DAVISON/GALVEZ...WPC (USA)

$$




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