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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1126Z Sep 19, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
726 AM EDT FRI SEP 19 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. TROPICAL WAVE
MOVED ACROSS THE FORECAST AREA EARLY THIS MORNING. THIS...IN
INTERACTION WITH A TUTT LOW OVER THE LEEWARD ISLES...TRIGGERED
SCATTERED DEEP CONVECTION ACROSS THE VIRGIN ISLES/EASTERN PUERTO
RICO AND CARIBBEAN SEA. AS THEY INTERACT... THIS SUSTAINS THE
NORTHWARD ADVECTION OF ITCZ MOISTURE ACROSS THE FRENCH ISLES TO
THE NORTHEAST CARIBBEAN. ALONG THIS TRAILING BAND...THE SATELLITE
DERIVED PWAT ANALYSIS SHOWS BETWEEN 50-60MM OF AVAILABLE WATER.
ANOTHER TROPICAL WAVE FOLLOWS...WITH AXIS ALONG 46W/47W EARLY THIS
MORNING.

ALOFT...TUTT LOW IS TO DOMINATE UPPER FLOW PATTERN INTO THE MEDIUM
RANGE PERIOD...WITH GLOBAL MODEL GUIDANCE SHOWING CLOSED LOW
MEANDERING BETWEEN THE NORTHERN LEEWARD/VIRGIN ISLES AND PUERTO
RICO. HOWEVER...THE INTERACTION BETWEEN THIS FEATURE AND ANOTHER
TUTT LOW THAT APPROACHES FROM THE EAST REMAINS TO BE
DETERMINED...WITH THE ECMWF SHOWING A DEEPER/BETTER ORGANIZED LOW
THAN THE GFS ESTABLISHING TO THE NORTH OF THE ISLANDS EARLY NEXT
WEEK. CONSIDERING HOW ACTIVE TUTT PATTERN HAS BEEN THUS FAR THIS
SEASON...THE DEEPER TUTT AS SUGGESTED BY THE ECMWF SEEMS A SAFER
BET. AT MID LEVELS... MODELS AGREE ON THEIR FORECAST OF AN
INVERTED TROUGH MEANDERING WEST ACROSS THE ISLAND CHAIN EARLY ON
SATURDAY MORNING...AND THROUGH SUNDAY MORNING PULLING ACROSS
PUERTO RICO TO THE MONA PASSAGE. THIS WILL COMBINE WITH TUTT
PATTERN ALOFT TO HELP SUSTAIN UNSETTLED WEATHER CONDITIONS ACROSS
THE FORECAST AREA. PWAT IS TO REMAIN AROUND 40-45MM DURING THE
NEXT FEW DAYS. THIS WILL FEED THE DIURNAL CONVECTIVE PATTERN/SEA
BREEZE CONVERGENCE...WITH LATE MORNING/AFTERNOON CONVECTION TO
GENERALLY PREVAIL ACROSS THE FORECAST AREA. ALTHOUGH HIGH
RESOLUTION MODELS SHOW MOST ACTIVE ACROSS WESTERN INTERIOR
PORTIONS OF PUERTO RICO...DEEP LAYER CONVECTIVE INSTABILITY AND
PREVAILING EASTERLIES WILL ALLOW FOR SOME DEVELOPMENT ACROSS THE
VI TO EASTERN PORTIONS OF PUERTO RICO. RAINFALL MAXIMA WILL PEAK
AT 3-5 INCHES... WITH MOST INTENSE ACROSS SAINT CROIX...EL YUNQUE
RAINFOREST AND WESTERN INTERIOR PORTIONS OF PUERTO RICO.

NEXT TROPICAL WAVE ENTERS THE FORECAST AREA ON MONDAY. IF UPPER
TUTT PATTERN EVOLVES AS INTENSE AS THE ECMWF SUGGESTS...IT COULD
RESULT IN ORGANIZED HEAVY CONVECTION AS IT PULLS ACROSS THE
FORECAST AREA.

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