Prognostic Meteorological Discussion
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FXCA20 KWBC 201149
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
648 AM EST TUE FEB 20 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 20/06
UTC: SATELLITE IMAGERY SHOWS A HIGHLY AMPLIFY LONG WAVE PATTERN
DOMINATING THE BASIN...WITH A LONG WAVE RIDGE EXTENDING FROM THE
WESTERN CARIBBEAN TO THE EASTERN USA-WESTERN ATLANTIC.
THIS...IN-TURN...SUSTAINS THE SOUTHWARD AMPLIFICATION OF A LONG
WAVE TROUGH TO THE EAST. THE TROUGH BOUNDS BETWEEN 30W-35W AND TO
THE NORTH OF 15N. AT LOW LEVELS THIS PROVIDES SUPPORT TO A SURFACE
FRONT THAT TRAILS NORTH OF THE ISLANDS ALONG 25N...WHILE ALSO
SUSTAINING A PREFRONTAL SHEAR LINE ACROSS THE VIRGIN ISLES TO
EASTERN PUERTO RICO. THE LATTER IS ENHANCING LOW LEVEL MOISTURE
CONVERGENCE WHILE ALSO FAVORING SCATTERED SHALLOW CONVECTION.

UNDER THE INFLUENCE OF THE RIDGE TO THE WEST...THE UPPER LEVEL
TROUGH IS TO GRADUALLY AMPLIFY FROM THE EAST...TO STRETCH ACROSS
THE GREATER ANTILLES AS THE WEEK WEARS ON. AS THE MID/UPPER LEVEL
TROUGH REPOSITIONS ACROSS THE FORECAST AREA...A JET MAXIMA TO THE
SOUTH IS TO RELOCATE FROM THE FRENCH/WINDWARD ISLES TO PUERTO
RICO/MONA PASSAGE LATER ON THURSDAY-EARLY FRIDAY MORNING. IN
RESPONSE...EXPECTING SHIFT FROM A STRONG UPPER CONVERGENT PATTERN
TO WEAK CONVERGENT/NEARLY NEUTRAL LATER IN THE WEEK. AT MID LEVELS
THIS WILL BE ACCOMPANIED BY AN INCREASED IN CYCLONIC VORTICITY
ADVECTION DURING THE WEEKEND. INFLOW OF SHORT WAVE ENERGY AND
WEAKENING OF THE TRADE WIND CAP COULD LEAD TO A MORE ACTIVE
PATTERN DURING THE WEEKEND. AT LOW LEVELS...UNDER INFLUENCE OF
MODIFYING POLAR RIDGE OVER THE WESTERN ATLANTIC...THE SURFACE
FRONT IS TO MEANDER TO THE WEST-SOUTHWEST...ENTERING THE VIRGIN
ISLES BY MIDMORNING ON WEDNESDAY...AND PULLING ACROSS PUERTO RICO
LATER IN THE DAY...MEANWHILE FAVORING A LOW LEVEL CONVERGENT
PATTERN THAT IS TO ENHANCE CONVECTIVE DEVELOPMENT. BUT LACKING
STRONG UPPER LEVEL SUPPORT...THE FRONTAL BOUNDARY IS TO THEN
FRONTOLIZE ON THURSDAY-FRIDAY. ALTHOUGH WEAKENING...A COOL
ADVECTIVE PATTERN IS TO PERSIST THROUGH THE END OF THE WEEK. THE
BROAD POLAR RIDGE TO THE NORTH IS TO ALSO FAVOR A TIGHT GRADIENT
ACROSS THE FORECAST AREA...WITH LOW LEVEL WINDS OF 25-30KT
EXPECTED THROUGHOUT THE CYCLE. PWAT CONTENT OF 1.0-1.25 INCHES IS
TO GENERALLY PERSIST...EXCEPT ON THURSDAY WHEN A DRYER POST
FRONTAL AIR MASS ENTRAINS FROM THE EAST.

ENHANCED LOW LEVEL FRONTAL CONVERGENCE ON WEDNESDAY WILL BRING
MODERATE CONVECTION TO THE VIRGIN ISLES-EASTERN/NORTHEASTERN
PORTIONS OF PUERTO RICO...WITH POTENTIAL FOR LOCALLY HEAVY
RAINFALL AMOUNTS ACROSS LUQUILLO-EL YUNQUE RAINFOREST AND POSSIBLY
THE SAN JUAN METRO AREA. ACROSS INTERIOR PORTIONS OF PUERTO RICO
EXPECTING LIGHT TO MODERATE RAINFALL AMOUNTS...WITH MOST INTENSE
OVER SOUTHWEST PORTIONS OF THE ISLAND. ON THURSDAY-EARLY FRIDAY
EXPECTING LESSER AMOUNTS AS THE SURFACE FRONT WANES...BUT ON
FRIDAY EVENING-SUNDAY THE MID LEVEL TROUGH IS LIKELY TO SUSTAIN
DEEPER CONVECTION AND HIGHER RAINFALL AMOUNTS ACROSS THE ENTIRE
FORECAST AREA.

DAVISON/GALVEZ...WPC (USA)

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