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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1131Z Jul 03, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
731 AM EDT FRI JUL 03 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL 03/11
UTC: LOW LEVEL MOISTURE CONTENT CONTINUES TO EBB AS A DRY SAHARAN
AIR LAYER (SAL) ENTRAINS FROM THE EAST. THIS COMBINES WITH MID
LEVEL RIDGE OVER THE NORTHEAST CARIBBEAN TO GENERALLY FAVOR FAIR
WEATHER CONDITIONS DURING THE DAY. LOW LEVEL
WINDS...HOWEVER...APPEAR STRONG ENOUGH TO FAVOR GENERATION OF A
FEW STREAMERS ACROSS THE VIRGIN ISLES-VIEQUES-CULEBRA THIS
AFTERNOON. THESE ARE TO ALSO AFFECT NORTHEAST PUERTO RICO...BUT
ONLY EXPECTING LIGHT TO TRACE RAINFALL AMOUNTS IN BRIEF PASSING
SHOWERS. MEASURABLE AMOUNTS...IF ANY...WILL LIMIT TO NORTHWEST
PORTIONS OF THE ISLAND.

ON SATURDAY THE ENVIRONMENTAL CONDITIONS ARE TO BECOME SOMEWHAT
MORE FAVORABLE AS THE SAL STARTS TO EBB AND A RETROGRESSING TUTT
INDUCES A WEAKNESS IN THE MID LEVEL HEIGHT FIELD. THE GLOBAL AND
REGIONAL MODELS...AS WELL AS THE EUROPEAN ENSEMBLE GUIDANCE...HAVE
BEEN TRENDING IN FAVOR OF A MORE ACTIVE PATTERN ACROSS WESTERN
INTERIOR PORTIONS OF PUERTO RICO. IN THIS AREA THE CONSENSUS OF
THE MODELS SHOW LOCALIZED MAXIMA RANGING BETWEEN 1-3
INCHES...WHICH SEEMS FEASIBLE GIVEN THE EVOLVING PATTERN.

ON SUNDAY MOISTURE CONTENT EBBS AHEAD OF A PROGRESSIVE TROPICAL
WAVE...WITH AXIS TO ENTER THE ISLAND CHAIN LATER IN THE DAY. THE
MODELS MADE SOME TIMING ADJUSTMENTS TO THIS FEATURE...NOW SHOWING
THE WAVE STREAMING ACROSS THE VIRGIN ISLES-EASTERN PUERTO RICO
EARLY ON MONDAY MORNING. A TRAILING PLUME OF MOISTURE IS TO THEN
QUICKLY LIFT ACROSS THE FORECAST AREA DURING THE DAY. ALTHOUGH
AGREEING ON THE TIMING...THE GFS AND ECMWF DIVERGE ON THE MOISTURE
CONTENT OF THIS PLUME AND IMPACT IT COULD HAVE ACROSS THE FORECAST
AREA. THE GFS REMAINS HIGHLY BIASED IN FAVOR OF HIGHER MOISTURE
CONTENT THAN THE ECMWF...WITH UKMET ABANDONING THE GFS IN FAVOR OF
A DRYER SOLUTION. ALOFT IS WHERE THE ANSWER LIES...WITH TUTT LOW
MEANDERING OVER THE NORTHEAST CARIBBEAN MOVING AWAY AS A MID LEVEL
RIDGE BUILDS FROM THE EAST ACROSS THE WESTERN ATLANTIC TO THE
NORTHERN CARIBBEAN. THIS IS THE SAME PATTERN WE HAVE BEEN SEEING
OVER THE LAST FEW WEEKS...WITH MID LEVEL PATTERN QUICKLY BECOMING
HOSTILE TO ORGANIZED CONVECTION AND DAMPENING DEVELOPMENT AS WAVES
STREAMS ACROSS THE FORECAST AREA.

DAVISON...WPC (USA)