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Tropical Discussion
 
(Latest Discussion - Issued 1118Z Aug 21, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
718 AM EDT THU AUG 21 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. TUTT ALOFT
CONTINUES TO PULL AWAY AS BUILDING CELL OF THE SUBEQUATORIAL RIDGE
EXPANDS ACROSS THE NORTHEAST CARIBBEAN ISLES. THE RIDGE ALOFT IS
VENTING DEEP CONVECTION IN ASSOCIATION WITH A TROPICAL DISTURBANCE
EAST OF THE LESSER ANTILLES. THE DISTURBANCE IS DRAWING ITCZ
MOISTURE NORTH TOWARDS THE FRENCH/LEEWARD ISLANDS...WITH
CONVECTIVE CELLS QUICKLY BUILDING WEST. SATELLITE DERIVED PWAT
ANALYSIS SHOWS MOISTURE POOLING ALONG 55W/56W...WITH MOISTURE
CONTENT PEAKING AROUND 75MM. THE NHC IS MONITORING THIS
SYSTEM...WITH MEDIUM RISK OF TROPICAL CYCLONE FORMATION OVER THE
NEXT TWO DAYS.

BUILDING UPPER LEVEL RIDGE IS TO EXPAND FARTHER WEST ACROSS THE
FORECAST AREA THROUGH FRIDAY EVENING. AS IT BUILDS...THIS IS TO
PROVIDE THE STEERING FLOW TO THE TROPICAL DISTURBANCE NEARING THE
ISLAND CHAIN. THE GFS AND ECMWF ARE IN CLOSE AGREEMENT WITH THIS
FEATURE...WITH BOTH FORECASTING AN OPEN TROUGH/FAIRLY STRONG
TROPICAL WAVE TO ENTER THE VI/EASTERN PUERTO RICO EARLY ON FRIDAY
MORNING. THIS IS TO QUICKLY MOVE ACROSS THE MONA PASSAGE INTO
EASTERN HISPANIOLA LATER IN THE DAY. THIS IS MUCH FASTER THAN
PREVIOUSLY ANTICIPATED. ALTHOUGH THE GLOBAL MODEL GUIDANCE ONLY
PROJECTS RAINFALL MAXIMA OF 2-3 INCHES AS IT ENTERS THE VI/EASTERN
PUERTO RICO...THE EARLY MORNING DEVELOPMENT PRESENTS A RISK OF AN
MCS FORMING OVER THE VIRGIN ISLES/EASTERN PUERTO RICO. SO THERE IS
A POTENTIAL FOR CONSIDERABLY HIGHER AMOUNTS. AS IT PULLS ACROSS
PUERTO RICO DURING THE DAY...EXPECTING MAXIMA OF 3-5 INCHES. IN A
SOUTHEASTERLY FLOW...THE MOST INTENSE IS TO CLUSTER ACROSS
NORTHWEST PUERTO RICO IN THE LATE MORNING/EARLY AFTERNOON HOURS.

DURING MEDIUM RANGE PERIOD...A RETROGRESSING TUTT IS TO PULL
ACROSS THE VIRGIN ISLES LATER ON SUNDAY. RIDGE TO THE NORTH IS TO
STEER THIS VORTEX ACROSS THE FORECAST AREA EARLY NEXT WEEK...WITH
GFS SHOWING FAIRLY STRONG MID LEVEL VORTEX OVER THE VIRGIN
ISLES/EASTERN PUERTO RICO. THE EUROPEAN MODEL...HOWEVER...SHOWS
THE VORTEX STREAMING JUST SOUTH OF THE FORECAST AREA. ALTHOUGH
THEY DISAGREE ON GENERAL TRAJECTORY...THEY ONLY SHOW LIGHT
CONVECTION DEVELOPING AS THE MID/UPPER PERTURBATION REACHES THE
FORECAST AREA.

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