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Tropical Discussion
 
(Latest Discussion - Issued 1140Z Jul 22, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
740 AM EDT TUE JUL 22 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. TUTT LOW
REMAINS NORTH OF THE FORECAST AREA WHILE CENTERING ON A CLOSED LOW
NEAR 26N 64W. A SECONDARY LOW TO THE WEST NOW CENTERS NEAR JAMAICA
WHILE EXTENDING A SHORT WAVE TROUGH TO PANAMA. ON ITS WAKE...A
RIDGE IS BUILDING ACROSS THE LESSER ANTILLES TO THE EASTERN
CARIBBEAN...WHERE IT SUSTAINS A TRADE WINDS CAP. AT LOW
LEVELS...WEAK PERTURBATION ON THE EASTERLY TRADES ENTERED THE
EASTERN CARIBBEAN EARLY THIS MORNING. THIS SUSTAINS SHALLOW
MOISTURE CONVERGENCE ACROSS THE ISLAND CHAIN...WITH CELLS QUICKLY
SPREADING ACROSS THE LEEWARD/VIRGIN ISLES TO EASTERN PUERTO RICO.
TD-TWO FOLLOWS...WITH THE NHC FORECASTING A SLOW NORTHWESTWARD
PROGRESSION OVER THE NEXT FEW DAYS. THEY EXPECT HOSTILE
ENVIRONMENTAL CONDITIONS TO PERSIST AND INHIBIT FURTHER
INTENSIFICATION OF THIS FEATURE.

THE EASTERLY WAVE MOVES ACROSS THE FORECAST AREA THROUGH THIS
EVENING... MEANWHILE TRIGGERING SHALLOW CONVECTION AS IT MOVES
ACROSS THE EASTERN CARIBBEAN. GLOBAL MODELS CONTINUE TO FORESEE
MOSTLY LIGHT RAINFALL AMOUNTS...WITH ACCUMULATION RANGING BETWEEN
TRACE AND QUARTER INCH ACROSS THE VIRGIN ISLES/EASTERN PUERTO
RICO. THE NMM VERSION OF THE HRWRF...HOWEVER...SHOWS MAXIMA OF
OVER AN INCH CLUSTERING OVER NORTHWEST PUERTO RICO DURING THE
AFTERNOON HOURS. BUT IT STANDS ALONE IN FORECASTING THESE AMOUNTS.
CONSIDERING THE CLOSE PROXIMITY OF THE UPPER TROUGH...AND LOW
LEVEL WINDS VEERING TO THE SOUTHEAST...THIS IS A POSSIBILITY WORTH
CONSIDERING.

THE NHC HAS TD-TWO OVER THE FRENCH ISLES EARLY ON THURSDAY
MORNING...THEN WEAKENING TO AN OPEN WAVE. GLOBAL MODELS THEN SHOW
REMNANTS OF THIS FEATURE QUICKLY PULLING ACROSS THE FORECAST AREA.
GLOBAL MODELS GENERALLY AGREE ON MEASURABLE RAINFALL AMOUNTS AS
THE PERTURBATION MOVES ACROSS THE FORECAST AREA...WITH MOST
INTENSE OVER THE VI/EASTERN PUERTO RICO. THIS IS GOING TO BE
HIGHLY DEPENDENT ON HOW TUTT ALOFT EVOLVES OVER THE NEXT FEW DAYS.
IF IT WERE TO HOLD...IT COULD THEN INTERACT WITH THE LOW LEVEL
PERTURBATION IN SUPPORT OF SCATTERED CONVECTION. BUT IF THE TROUGH
PULLS AWAY...WE WOULD QUICKLY LOOSE THE UPPER SUPPORT RESULTING IN
LESSER AMOUNTS. AS A RESULT...GLOBAL MODELS DIVERGE ON HOW MUCH
RAINFALL TO EXPECT...WITH THE GFS AND UKMET APPEARING MORE
OPTIMISTIC THAN THE ECMWF. EITHER WAY...IT SHOULD BRING WELCOME
RELIEF TO DROUGHT CONDITIONS OVER THE ISLANDS.

FIGUEROA...MARN (EL SALVADOR)
VALVERDE...IMN (COSTA RICA)
DAVISON...WPC (USA)