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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1117Z Jul 17, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
717 AM EDT THU JUL 17 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. BROAD CELL OF
THE SUBTROPICAL RIDGE DOMINATES FLOW ACROSS THE ATLANTIC BASIN AS
IT ANCHORS ON A CLOSED HIGH NEAR 34N 52W. THIS RIDGE SUSTAINS A
BRISK EASTERLY FLOW ACROSS THE ISLAND CHAIN...WHILE ADVECTING
SHALLOW MOISTURE ACROSS THE LEEWARD ISLES. MID LEVEL CAP INVERSION
IS TRAPPING THIS MOISTURE BELOW 750/800 HPA. A TROPICAL WAVE ALONG
53W EMBEDS IN THIS FLOW...WITH THE MOST ACTIVE CONVECTION WITH
THIS WAVE DEVELOPING ALONG THE ITCZ. A DUST/HAZE LAYER TRAILS THIS
WAVE.

AT UPPER LEVELS...MODELS CONTINUE TO FORECAST A TUTT OVER THE
CENTRAL ATLANTIC TO RETROGRESS JUST NORTH OF THE FORECAST AREA
DURING THE WEEKEND...AND THEN HOLD THROUGH EARLY NEXT WEEK WHILE
ANCHORING ON A WELL DEFINED CYCLONIC CIRCULATION. AT MID LEVELS A
NARROW RIDGE EXTENDS WEST ACROSS THE NORTHEAST CARIBBEAN ISLES. AS
TUTT ALOFT RETROGRESSES TO THE WESTERN ATLANTIC IT IS TO PRESS
AGAINST THIS AXIS...SUSTAINING A GRADUAL EROSION THROUGH THE END
OF THE WEEK. ALTHOUGH RIDGE TENDS TO WEAKEN...MODEL GUIDANCE
SUSTAINING CAP INVERSION ACROSS THE FORECAST AREA. AT LOW LEVELS A
BROAD RIDGE IS TO GENERALLY HOLD ACROSS THE ATLANTIC BASIN. THE
TROPICAL WAVE IS TO ENTER THE ISLAND CHAIN AROUND 12UTC ON
FRIDAY...REACHING THE USVI/VIEQUES-CULEBRA AROUND 00UTC ON
SATURDAY. THROUGH THE NIGHT IT WILL MOVE ACROSS PUERTO
RICO...REACHING THE MONA PASSAGE BY FIRST LIGHT. DEEP MOISTURE
CONVERGENCE WITH THIS FEATURE IS EXPECTED TO THE SOUTH OF
15N...WITH SHALLOW MOISTURE TO CLUSTER ACROSS THE VI/EASTERN
PUERTO RICO. BUT IN A MOSTLY UNFAVORABLE ENVIRONMENT THE GLOBAL
MODEL GUIDANCE ONLY SHOWING LIGHT RAINFALL AMOUNTS...WITH MAXIMA
PEAKING AT 10-15MM IN ISOLATED CONVECTION.

IN THE ABSENCE OF MESO-SYNOPTIC FORCING...MODELS THEN SHOW LIGHT
SHOWERS AFFECTING THE VI-EASTERN PUERTO RICO FROM TIME TO TIME AS
STREAMERS DEVELOP ACROSS THE LEEWARD ISLES...AND THE OCCASIONAL
SHALLOW CLOUD CLUSTER PULLING ACROSS THE FORECAST AREA.

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