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The Weather Prediction Center
 
Tropical Discussion
 
(Latest Discussion - Issued 1158Z Dec 26, 2018)
 
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Abbreviations and acronyms used in this product


TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
658 AM EST WED DEC 26 2018

LAST NO AMENDS...THIS PRODUCT WILL NOT BE UPDATED WHILE THE
GOVERNMENT IS IN PARTIAL SHUTDOWN MODE.

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 26/06
UTC: IN A SEASONAL PATTERN...THE FORECAST AREA LIES UNDER THE
CONVERGENT/SUBSIDENT SIDE OF A MID/UPPER LEVEL RIDGE ENVELOPING
THE WESTERN ATLANTIC-CARIBBEAN BASIN. THIS IS CAPPING MOISTURE TO
THE LOWER LEVELS OF THE ATMOSPHERE. AT LOW LEVELS...LIGHT TO
MODERATE EASTERLY TRADES ENVELOP THE FORECAST AREA...FAVORING
EARLY MORNING SHOWERS ACROSS THE VIRGIN ISLES INTO THE CARIBBEAN
AND ATLANTIC COASTAL WATERS OF THE ISLAND.

ALOFT...A SHORT WAVE TROUGH IS TO PROPAGATE ALONG THE NORTHERN
FRINGES OF THE SUBEQUATORIAL RIDGE...TO STREAM ACROSS THE GULF OF
MEXICO TO THE BAHAMAS EARLY ON THURSDAY. DURING THE DAY ON FRIDAY
THIS IS TO STREAM ACROSS THE NORTHEAST FORECAST AREA. AS IT MOVES
TO THE EASTERN FRINGES OF THE UPPER LEVEL RIDGE...THE TROUGH IS TO
THEN DEEPEN ACROSS THE EASTERN CARIBBEAN. AT MID LEVELS...BROAD
CELL OF THE SUBTROPICAL  RIDGE IS TO DOMINATE THE WESTERN
ATLANTIC-NORTHERN CARIBBEAN. AS THE AFOREMENTIONED PERTURBATION
REVOLVES AROUND THIS AXIS...EXPECTING A SLIGHT INCREASE IN MID
LEVEL POSITIVE/CYCLONIC VORTICITY ADVECTION BY MIDDAY ON FRIDAY.
IN A COOLER ADVECTIVE PATTERN...THIS IS TO FAVOR DEEPER LAYER
CONVECTIVE INSTABILITY.

AT LOW LEVELS...HIGH/RIDGE ROLLS ACROSS THE EASTERN USA TO THE
WESTERN ATLANTIC EARLY IN THE CYCLE...TIGHTENING THE PRESSURE
GRADIENT WHILE FAVORING GRADUAL INTENSIFICATION OF THE EASTERLY
TRADES. AT 850 HPA THE WINDS ARE TO GRADUALLY INCREASE TO 30-40KT
WHILE BACKING TO THE EAST-NORTHEAST ON FRIDAY...THEN START TO
SLOWLY WEAKEN LATER DURING THE WEEKEND AS PREVAILING EASTERLY
TRADES RETURN TO THE FORECAST AREA. THE STRONGER WINDS WILL BE
ACCOMPANIED BY AN INCREASE IN LOW LEVEL MOISTURE
CONVERGENCE...GENERATION OF TRADE WIND SHOWERS...AND FAVOR THE
FORMATION OF DAYTIME STREAMERS ACROSS THE VIRGIN ISLES. DURING
THAT PERIOD EXPECTING MOST ACTIVE CONVECTION TO AFFECT THE
FORECAST AREA. OTHERWISE...SEASONAL SHOWERS ARE TO PREVAIL.

TROPICAL DISCUSSION FROM DEC 26/12 UTC: NOT ISSUED

TROPICAL/EASTERLY WAVES/TRADE WIND SURGES FROM 00 UTC:
INITIAL 24    36    48    60    72    84    96    TYPE     SOF
NONE

DAVISON...WPC (USA)