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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1043Z Jun 15, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
643 AM EDT FRI JUN 15 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUN 15/06
UTC: MID/UPPER LEVEL RIDGE ENVELOPING THE FORECAST AREA CONTINUES
TO WEAKEN UNDER PRESSURE FROM AN AMPLIFYING TROUGH TO THE
NORTH...WHILE A TUTT TO THE EAST STARTS TO LIFT AS THE RIDGE
WEAKENS. REMNANTS OF THE TUTT ARE TO BRIEFLY MEANDER WEST INTO THE
NORTHEAST CARIBBEAN EARLY IN THE CYCLE...ENHANCING LOW LEVEL
MOISTURE CONVERGENCE WHILE FAVORING SHALLOW CONVECTIVE
INSTABILITY. DEEPER INSTABILITY...HOWEVER...IS EXPECTED BY MIDDAY
ON SATURDAY AS THE RIDGE CRUMBLES AND TROUGH ESTABLISHES AS THE
DOMINANT FEATURE. DURING THIS PERIOD THE TRADE WINDS CAP
ENVELOPING THE FORECAST AREA IS TO RELAX ITS FOOTHOLD. AT LOW
LEVELS...PATTERN RESPONDS IN KIND...WITH WANING SUBTROPICAL RIDGE
NORTH OF THE ISLANDS SPLITTING IN TWO CELLS. THE WESTERNMOST WILL
CONFINE TO THE GULF OF MEXICO/FLORIDA PENINSULA...WHILE THE
EASTERNMOST SETTLES OVER THE CENTRAL ATLANTIC. IN RESPONSE TO
THIS...AND MEANDERING TROUGH TO THE NORTH...LOW-MID LEVEL WINDS
ARE EXPECTED TO GRADUALLY VEER TO THE SOUTHEAST. THIS WILL ENHANCE
MOISTURE TRANSPORT ACROSS THE ISLAND CHAIN...WITH PLUME OF
MOISTURE REACHING THE FORECAST AREA BY MIDDAY ON SATURDAY. DURING
THAT PERIOD PWAT CONTENT IS FORECAST TO PEAK AT 1.50-1.75 INCHES.
THE INFLOW OF MOISTURE WILL FEED AN INCREASE IN CONVECTION ACROSS
THE ENTIRE FORECAST AREA...WITH MOST ACTIVE EXPECTED ACROSS
NORTHWEST PUERTO RICO IN A DIURNAL PATTERN ON SATURDAY-SUNDAY.
NOTE THAT BOTH THE GFS AND ECMWF CONTINUE TO SHOW PEAK IN
CONVECTIVE INSTABILITY FOR THESE DAYS...WITH GDI FORECAST
SUGGESTING POTENTIAL FOR HIGHER RAINFALL AMOUNTS THAN WHAT THE
GLOBAL AND REGIONAL MODELS SUGGEST. THUS OUR QPF GUIDANCE FOR THE
PERIOD REMAINS HIGHER THAN WHAT THE MODELS FORECAST.

PER THE LATEST MODEL GUIDANCE...LINGERING MOISTURE IS TO FAVOR
LIGHTER CONVECTION DURING THE DAY ON MONDAY...WITH A DRYER AIR
MASS TO THEN ENTRAIN FROM THE EAST AHEAD OF A TROPICAL WAVE
STREAMING TOWARDS THE ISLANDS. THE WAVE ENTERS THE ISLAND CHAIN ON
MONDAY EVENING...AND DURING THE DAY ON TUESDAY IT IS TO STREAM
ACROSS THE EASTERN CARIBBEAN. AS IT NEARS THE FORECAST AREA THE
WAVE WILL PHASE WITH DIGGING MID/UPPER LEVEL TROUGH OVER THE
WESTERN ATLANTIC. AS THEY INTERACT...THE GLOBAL MODELS
CONSISTENTLY SHOW A DEEPER PLUME OF MOISTURE TO LIFT ACROSS THE
EASTERN CARIBBEAN...WITH MOISTURE POOLING OVER THE CARIBBEAN
COASTAL WATERS OF PUERTO RICO LATER ON TUESDAY EVENING THROUGH
WEDNESDAY. THIS COULD POTENTIALLY TRIGGER MODERATE TO HEAVY
RAINFALL AMOUNTS ACROSS THE ENTIRE FORECAST AREA...WITH THE
GFS-ECMWF GDI FORECAST SHOWING AN ENHANCED RISK OF SHOWERS AND
THUNDERSTORMS DURING THIS PERIOD.

DAVISON...WPC (USA)