Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center
 
Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1056Z Jul 17, 2018)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product


TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
656 AM EDT TUE JUL 17 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL 17/06
UTC: AT 250 HPA...A SHORT WAVE RIDGE IS INITIALIZED OVER THE
EASTERN CARIBBEAN...WHILE A DEEPENING TUTT LIES TO THE NORTH. IN
THIS PATTERN...A FAIRLY STRONG TRADES WINDS CAP ENVELOPS THE
NORTHEAST CARIBBEAN ISLES...WITH SHALLOW MOISTURE CONFINING TO
LOWER LEVELS OF THE ATMOSPHERE. THE METEOSAT AND GOES-16 IMAGERY
SHOWS A DRY SAHARAN AIR LAYER ENTRAINING ACROSS THE ISLAND
CHAIN...AND THIS WILL RESULT IN GRADUAL EROSION OF AVAILABLE
MOISTURE DURING THE AFTERNOON INTO THE EVENING HOURS.
MEANWHILE...ENOUGH MOISTURE REMAINS TO SUSTAIN A SECOND ROUND OF
CONVECTION DURING THE DAY TODAY. MOST ACTIVE IS EXPECTED OVER
WESTERN PUERTO RICO DURING THE AFTERNOON HOURS...WITH HIGHER
RESOLUTION MODELS SHOWING MAXIMA OF 1-2 INCHES. A BROAD TROPICAL
WAVE FOLLOWS...WITH AXIS SPANNING BETWEEN 50W-40W EARLY THIS
MORNING.

AS PREVIOUSLY INDICATED...THE UPPER LEVEL TROUGH IS TO BECOME
DOMINANT FEATURE ACROSS THE NORTHEAST CARIBBEAN BY MIDWEEK.
ALTHOUGH WELL DEFINED...THIS WILL BE SLOW TO OVERCOME NEGATIVE
INFLUENCE OF MID LEVEL TRADE WINDS CAP ENVELOPING THE NORTHEAST
CARIBBEAN ISLES. THIS ABRUPTLY CHANGES LATER ON WEDNESDAY/EARLY ON
THURSDAY MORNING...WHEN A MOIST PLUME LEADING THE TROPICAL WAVE
MOVES INTO THE EASTERN CARIBBEAN. AS THE WAVE PHASES WITH THE
TROUGH ALOFT...TRADE WINDS CAP WILL RELAX ITS FOOTHOLD ACROSS THE
FORECAST AREA...WITH PWAT CONTENT PEAKING BETWEEN 1.75-2.0 INCHES
BY MIDDAY ON THURSDAY. AS THEY INTERACT...SCATTERED RAIN SHOWERS
ARE EXPECTED ACROSS THE VIRGIN ISLES-EASTERN PUERTO RICO DURING
THE MORNING HOURS ON THURSDAY...TO FAVOR LIGHT TO MODERATE
RAINFALL AMOUNTS. ACTIVITY WILL THEN BUILD INLAND ACROSS PUERTO
RICO AS ENHANCED BY THE DIURNAL HEAT CYCLE. FOLLOWING WAVE
PASSAGE...A DEEP LAYER SOUTHEASTERLY FLOW IS TO ESTABLISH. THIS
WILL ENHANCE MOISTURE CONVERGENCE ACROSS NORTHWEST PUERTO RICO
DURING THE AFTERNOON HOURS. THE HIGH MOISTURE CONTENT AND
FAVORABLE UPPER DYNAMICS WILL LIKELY RESULT IN AREAS OF MODERATE
TO HEAVY RAINFALL AMOUNTS. DURING THIS PERIOD THE GFS SEEMS TO
HAVE A BETTER HANDLE OF THE SITUATION THAN THE UKMET AND ECMWF
GLOBAL MODELS. OTHER CONVECTION IS EXPECTED TO BUILD BETWEEN EL
YUNQUE AND THE SOUTHERN HALF OF THE SAN JUAN METRO AREA...WITH
POTENTIAL FOR MODERATE/LOCALLY HEAVY RAINFALL AMOUNTS AS SHOWERS
TRAIN ACROSS TRUJILLO ALTO-SOUTHERN SAN JUAN/GUAYNABO TO TOA ALTA.
ACTIVITY IS TO PERSIST THROUGH EARLY MORNING HOURS ON
FRIDAY...THEN GRADUALLY WANE AS TRAILING SAHARAN AIR LAYER
ENTRAINS FROM THE EAST AND TRADE WINDS CAP STRENGTHENS AGAIN.

A SHARP DROP IN ACTIVITY IS EXPECTED ON FRIDAY-SUNDAY AS TRAILING
SAHARAN AIR LAYER ENTRAINS ACROSS THE FORECAST AREA...SUSTAINING A
SHARP DROP IN MOISTURE CONTENT. DURING THIS PERIOD...ACTIVITY WILL
LIMIT TO STREAMERS FORMING OVER THE VIRGIN
ISLES-VIEQUES-CULEBRA...TO AFFECT EASTERN PUERTO RICO FROM
TIME-TO-TIME. IN EASTERLY FLOW...SHALLOW AFTERNOON CONVECTION WILL
THEN BUILD ACROSS WESTERN PUERTO RICO.

DAVISON...WPC (USA)