Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
657 AM EST MON JAN 22 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 22/06
UTC: FORECAST AREA LIES ON THE CONVERGENT SIDE OF A MID/UPPER
LEVEL RIDGE THAT EXTENDS OVER THE EASTERN CARIBBEAN...WITH MID
LEVEL AXIS CENTERING ON A CLOSED HIGH THAT MEANDERS BETWEEN PUERTO
RICO AND THE VIRGIN ISLES. THE RIDGE FAVORS A FAIRLY STRONG TRADE
WINDS CAP ACROSS THE FORECAST AREA. A SHORT WAVE TROUGH TO THE
NORTHWEST IS STREAMING ACROSS THE BAHAMAS EARLY THIS MORNING. THE
RIDGE IS TO STEER THIS VORTEX JUST NORTH OF PUERTO RICO LATER THIS
EVENING...AND AS IT CLEARS THE FRINGES OF THE RIDGE ON TUESDAY IT
IS TO THEN AMPLIFY ACROSS THE TROPICAL ATLANTIC. ON ITS WAKE...THE
MID LEVEL RIDGE IS TO STRENGTHEN ITS FOOTHOLD ACROSS THE NORTHEAST
CARIBBEAN. AN ELEVATED CAP INVERSION IS TO THEN PREVAIL THROUGH
THE END OF THE WEEK.

AT LOW LEVELS...BROAD RIDGE DOMINATES THE FLOW ACROSS THE WESTERN
ATLANTIC INTO THE CARIBBEAN BASIN...FAVORING A TIGHT GRADIENT AND
BRISK EASTERLY TRADES. THESE ARE STRONG ENOUGH TO FAVOR GENERATION
OF STREAMERS ACROSS THE VIRGIN ISLES THAT AFFECT EASTERN PUERTO
RICO FROM TIME-TO-TIME. ALSO AT LOW LEVELS...A SAGGING FRONT LIES
TO THE NORTH OF PUERTO RICO AND HISPANIOLA. THIS BOUNDARY IS THE
FOCUS OF LOW LEVEL MOISTURE CONVERGENCE...AND IN INTERACTION WITH
THE MID LEVEL TROUGH IT SUSTAINS ORGANIZED DEEP CONVECTION ACROSS
THE BAHAMAS EARLY THIS MORNING. SIMILAR PATTERN IS EXPECTED TO THE
NORTH OF THE FORECAST AREA LATER TODAY AS THE MID LEVEL VORTEX
STREAMS TO THE NORTH LATER THIS EVENING. BOUNDARY IS TO THEN
DISSIPATE ON TUESDAY-WEDNESDAY. SIMULTANEOUSLY...A POLAR FRONT
STREAMING ACROSS THE CENTRAL TO THE EASTERN USA ON TUESDAY IS TO
THEN PRESS AGAINST THE LOW LEVEL RIDGE. THE RIDGE WILL YIELD TO
THE POLAR TROUGH...WEAKENING AS IT RELOCATES TO THE CENTRAL
ATLANTIC. AS THE PRESSURE GRADIENT SLACKENS LIGHTER EASTERLY
TRADES ARE TO THEN PREVAIL THROUGH FRIDAY MORNING. AS THE WINDS
WEAKENS...THE INCIDENCE OF STREAMERS FORMING OVER THE VIRGIN ISLES
AND AFFECTING EASTERN PUERTO RICO IS EXPECTED TO DECREASE THROUGH
AT LEAST FRIDAY MORNING. HOWEVER...THE LIGHTER WINDS WILL ALLOW
FOR SHALLOW MOISTURE TO POOL ACROSS THE NORTHEAST CARIBBEAN...WITH
PWAT CONTENT FORECAST TO PEAK AROUND 1.50 INCHES ON TUESDAY
AFTERNOON THROUGH THURSDAY MORNING. THIS WILL THEN FEED DIURNAL
CONVECTION BUILDING ACROSS THE FORECAST AREA...WITH THE NAM AND
REGIONAL HRWRF SHOWING POTENTIAL FOR MODERATE TO HEAVY CONVECTION
ACROSS WESTERN PUERTO RICO ON TUESDAY AND WEDNESDAY.

LATER IN THE WEEK...POLAR FRONT IS TO MEANDER EAST ACROSS THE
WESTERN ATLANTIC. THIS WILL SUSTAIN A PREFRONTAL SHEAR LINE THAT
MOVES OVER PUERTO RICO LATER ON FRIDAY...WHERE IT IS TO MEANDER
THROUGH AT LEAST SUNDAY AFTERNOON. AS THE SHEAR LINE ENTERS THE
FORECAST AREA EXPECTING WINDS TO SURGE...WITH GFS SHOWING 850 HPA
WINDS OF AROUND 30KT. THE STRONGER WINDS ARE TO PERSIST THROUGHOUT
THE WEEKEND INTO EARLY NEXT WEEK. IN A COOL ADVECTIVE
PATTERN...THE BRISK NORTHEASTERLY WINDS WILL FAVOR GENERATION OF
TRADE WIND SHOWERS ACROSS THE FORECAST AREA...TO RESULT IN LIGHT
RAINFALL AMOUNTS IN PASSING SHOWERS. THERE IS...HOWEVER...A SLIGHT
RISK OF ECHO TRAINING ALONG THE SHEAR LINE.

DAVISON/GALVEZ...WPC (USA)

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