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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1012Z May 18, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 AM EDT FRI MAY 18 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 18/06
UTC: MID-LEVEL RIDGE EXTENDS AN AXIS ALONG 73W...FROM NORTHERN
COLOMBIA ACROSS HAITI INTO THE NORTHWESTERN ATLANTIC. TO THE
EAST...A LARGE TROUGH EXTENDS ACROSS THE TROPICAL ATLANTIC
CENTERING A LOW AT 26N 47W. THIS TROUGH EXTENDS A BROAD AXIS TO
THE WEST-SOUTHWEST INTO THE NORTHEASTERN CARIBBEAN. THE PRESENCE
OF THIS TROUGH IS DESTABILIZING THE TRADE WIND CAP IN AREAS EAST
OF THE LEEWARD ISLANDS...WHICH IS ALLOWING SOME VERTICAL
DEVELOPMENT OF SHALLOW CONVECTION TO OVER 700 HPA. THE SAN JUAN
00Z SOUNDING SHOWS THE CAP SITTING AT 720 HPA. ALTHOUGH THE
BOUNDARY LAYER IS MOIST...A SIGNIFICANT AMOUNT OF DRY AIR SITS
OVER IT. THE TRADE WINDS ARE STRAIGHT FROM THE EAST AT 20-25KT.
THIS IS LEADING TO THE STREAMING OF TRADE WIND SHOWERS FROM EAST
TO WEST.

MODELS ARE SUGGESTING PATTERN TO PERSIST DURING THE NEXT FEW DAYS.
UNDER THE INFLUENCE OF DRY AIR BUT DESTABILIZATION ASSOCIATED WITH
THE TROUGH...AND PERSISTENT FAST EASTERLY TRADES...EXPECTING
RAPIDLY PASSING MODERATE TRADE WIND SHOWERS. MODELS AGREE ON A
TRANSIENT PEAK IN ACTIVITY ON SATURDAY...AS A SHORT WAVE TROUGH
AXIS CROSSES THE ISLANDS FROM NORTHEAST TO SOUTHWEST. THIS WILL
ENTER IN PHASE WITH THE DIURNAL CYCLE OF CONVECTION TO SUSTAIN
MODERATE PRECIPITATION. UNDER THE INFLUENCE OF STREAMERS AND ECHO
TRAINING OF SHALLOW CONVECTION...EXPECTING ACCUMULATIONS PEAKING
AT 1-1.5 INCHES ALONG THE NORTHERN SLOPES OF THE CENTRAL AND
WESTERN CORDILLERA DURING SATURDAY. OTHERWISE...CONVECTION IS
EXPECTED ON A DAILY BASIS PEAKING IN EASTERN PUERTO RICO AND THE
VI IN MORNING HOURS AND WESTERN/NORTHWESTERN PUERTO RICO DURING
THE AFTERNOON.


HUDSON...MS (JAMAICA)
NIXON...BDM (THE BAHAMAS)
DAVISON/GALVEZ...WPC (USA)