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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1129Z Sep 26, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
729 AM EDT FRI SEP 26 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. A CLOSED LOW
NOW CENTERS JUST NORTH OF THE VI...WHILE AN AMPLIFYING TUTT
CONTINUES TO FOCUS SHORT WAVE ENERGY/CYCLONIC VORTICITY ACROSS THE
NORTHEAST CARIBBEAN ISLANDS. THIS IS COMBINING WITH ABOVE NORMAL
SST TO FAVOR GENERATION OF SCATTERED DEEP CONVECTION. DEEP TUTT
PATTERN ALOFT IS INDUCING AN INVERTED TROUGH IN THE EASTERLY
TRADES. THIS EXTENDS NORTH ALONG 64W/65W AND ACROSS THE VIRGIN
ISLES TO THE TROPICAL ATLANTIC. THIS FAVORS A MOIST
SOUTH-SOUTHEAST FLOW ACROSS THE ISLAND CHAIN...ENHANCING MOISTURE
TRANSPORT/CONVERGENCE ACROSS THE FORECAST AREA.

MODELS FORECAST THE TUTT LOW TO MOVE OVER PUERTO RICO EARLY THIS
MORNING...AND REMAIN OVER THE FORECAST AREA THROUGH AT LEAST
MIDMORNING ON SATURDAY. MEANWHILE...THIS IS TO CONTINUE FOCUSING
SHORT WAVE ENERGY/ CYCLONIC VORTICITY ACROSS THE FORECAST AREA.
LATER DURING THE WEEKEND...A BUILDING CELL OF THE SUBEQUATORIAL
RIDGE IS TO SLOWLY DISPLACE THIS AXIS WEST AND NORTH. BUT THIS IS
GOING TO BE A SLOW TO EVOLVE PATTERN...SO FORECAST AREA IS LIKELY
TO REMAIN ON THE DIVERGENT SIDE OF UPPER TROUGH. BEST MID LEVEL
FORCING...HOWEVER...IS EXPECTED THROUGH MIDDAY ON SATURDAY. AT LOW
LEVELS...THE MOIST SOUTHERLY FLOW IS TO PERSIST THROUGH MONDAY
MORNING. THIS IS TO HELP SUSTAIN HIGH PWAT AMOUNTS OF NEARLY TWO
INCHES ACROSS THE FORECAST AREA THROUGH SATURDAY EVENING/EARLY
SUNDAY MORNING.

ALTHOUGH UNFOLDING AT A SLOWER PACE THAN PREVIOUSLY
ANTICIPATED...STRONG DYNAMICAL FORCING WILL COMBINE WITH DIURNAL
HEATING/SEA BREEZE CONVERGENCE TO SUSTAIN A SURGE IN CONVECTION
THROUGH THE DAY. GLOBAL MODELS MADE SOME CORRECTIONS...AND HOW
SHOWING CONSIDERABLY HIGHER AMOUNTS ACROSS THE NORTHEAST
CARIBBEAN. BUT CONSIDERING EVOLVING PATTERN AND STRONG UPPER
FORCING...IT LOOKS LIKE THEY ARE TOO FAR TO THE EAST AND
DOWNPLAYING POTENTIAL FOR LAND/SEA INTERACTION ACROSS PUERTO RICO.
IN A SOUTHWESTERLY MID/UPPER LEVEL SHEAR CONDITIONS...EXPECTING
MOST ACTIVE CONVECTION BETWEEN THE VIRGIN ISLES AND EASTERN PUERTO
RICO EARLY THIS MORNING. THE SAN JUAN METRO AREA IS LIKELY TO
EXPERIENCE THE BRUNT OF THE CONVECTION LATER THIS MORNING THROUGH
THE AFTERNOON HOURS...WITH RAINFALL MAXIMA EXPECTED TO PEAK AT 3-5
INCHES. ALONG THE NORTH COAST AND WESTERN INTERIOR PORTIONS OF
PUERTO RICO THE MAXIMA SHOULD PEAK AT 1-3 INCHES. STRONG SHEAR
ENVIRONMENT AND COLD ADVECTION ALOFT ARE ALSO LIKELY TO RESULT IN
SOME SEVERE CONVECTIVE CELLS DEVELOPING/WATER SPOUTS AND POTENTIAL
FOR SMALL HAIL. ALTHOUGH UNSETTLED WEATHER CONDITIONS ARE EXPECTED
THROUGH THE WEEKEND...THEY WILL BECOME MORE DEPENDENT ON DIURNAL
CYCLE RATHER THAN ON THE WEAK UPPER FORCING.

VALVERDE...IMN (COSTA RICA)
MEDINA...ONAMET (REPUBLICA DOMINICANA)
DAVISON...WPC (USA)