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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1145Z Jul 08, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
745 AM EDT WED JUL 08 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL 08/12
UTC: A TROPICAL WAVE CROSSED THE FORECAST AREA OVERNIGHT...WITH
AXIS REACHING EASTERN HISPANIOLA EARLY THIS MORNING. ON ITS
WAKE...A MOIST SOUTHEASTERLY FLOW PERSISTS ACROSS THE ISLAND
CHAIN/EASTERN CARIBBEAN. THE INFLOW OF MOISTURE WILL FEED
SECONDARY DEVELOPMENT DURING THE DAY TODAY...WITH MOST ACTIVE
CLUSTERING OVER NORTHWEST PUERTO RICO LATER THIS MORNING/EARLY
AFTERNOON HOURS. ENVIRONMENTAL CONDITIONS ARE TO THEN GROW HIGHLY
UNFAVORABLE FOR DEVELOPMENT AS A TRAILING SAHARAN AIR LAYER
ENTRAINS FROM THE EAST. THIS WILL COMBINE WITH MEANDERING MID
LEVEL RIDGE TO HELP SUSTAIN A DRYING TREND ON THURSDAY...TO
SUSTAIN FAIR WEATHER CONDITIONS ACROSS THE ENTIRE FORECAST AREA.

LATER ON THURSDAY/EARLY ON FRIDAY MORNING A WEAKER TROPICAL WAVE
STREAMS ACROSS THE FORECAST AREA. BUT IT LOOKS LIKE THIS WAVE WILL
HAVE A HARD TIME OVERCOMING THE NEGATIVE INFLUENCE OF THE
LINGERING SAHARAN AIR LAYER AND PERSISTENT MID LEVEL TRADE WINDS
CAP. AS A RESULT...ONLY EXPECTING A FEW SHOWERS WITH THIS FEATURE
AS IT STREAMS ACROSS THE FORECAST AREA DURING THE MORNING HOURS ON
FRIDAY...WITH MOST ACTIVE TO AFFECT EASTERN PUERTO RICO AND THE
VIRGIN ISLES.

A STRONGER TROPICAL WAVE WILL FOLLOW DURING THE WEEKEND...WITH
PWAT CONTENT OF NEARLY TWO INCHES AS IT REACHES THE VIRGIN
ISLES/EASTERN PUERTO RICO LATER ON SATURDAY/EARLY ON SUNDAY
MORNING. ALTHOUGH AGREEING ON THE TIMING OF THIS WAVE...THE MODELS
DIVERGE ON ITS IMPACT OVER THE FORECAST AREA. THE GFS...IN
CONTRAST TO THE ECMWF AND UKMET...FORESEES A STRONGER MID LEVEL
REFLECTION OF THIS FEATURE...AND AS A RESULT IT SHOWS LONGER
LASTING/CONSISERABLY HIGHER RAINFALL AMOUNTS. ALTHOUGH THE GFS
SEEMS TO BE A BIT OVERDONE WITH THIS FEATURE...THE BACKEND OF AN
ATMOSPHERIC KELVIN WAVE IS TO STREAM ACROSS THE EASTERN CARIBBEAN
DURING THE WEEKEND. THIS MIGHT BE ENOUGH TO RESULT IN MEASURABLE
RAINFALL AMOUNTS...BUT IT WILL BE FOR A SHORTER WINDOW OF TIME AS
THE MJO PATTERN IS TO TRANSITION TO ITS CONVERGENT PHASE EARLY
NEXT WEEK..

DAVISON...WPC (USA)