Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 041351
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
951 AM AST TUE AUG 4 2015

.DISCUSSION...DRY CONDITIONS AGAIN TODAY. A FEW SHOWERS ARE MOVING
WESTWARD ON THE ATLANTIC NORTH OF CULEBRA/SAINT THOMAS BUT EXPECT
THESE TO STAY NORTH OF PUERTO RICO IN THE AFTERNOON. 12Z TJSJ
SOUNDING ARRIVED SHOWING A DAUNTING 5.5C INVERSION BETWEEN 830MB
AND 800 MB WITH A DEW POINT IMMEDIATELY DROPPING OFF TO -3.6C...
AND ANOTHER INVERSION JUST ABOVE 600 MB...FRAMING THE SAHARAN AIR
ALOFT. SAHARAN AIR WILL BEGIN EXITING TOWARDS THE WEST LATE TODAY
BUT MOISTURE IS NOT EXPECTED TO IMPROVE FOLLOWING THE BRIEF TONGUE
OF MOISTURE CURRENTLY PRODUCING THE SHOWERS NORTH OF THE ISLANDS.

DECREASED THE PROBABILITY AND COVERAGE OF SHOWERS ACROSS THE
ISLANDS TODAY IN UPDATE AS THE SAHARAN AIR WILL REDUCE CHANCES OF
DEVELOPMENT. THOSE THAT DO WILL BE VERY BRIEF AND LIGHT...MAINLY
FOR SOUTHWEST PUERTO RICO MOUNTAINS AND OVER ATLANTIC WATERS.

&&

.AVIATION...VFR XPCTD THRU WED XCP IN SCT SHRA/TSRA WEST PR INCL
TJMZ WED AFT. WINDS BLW FL100-SFC E-ENE 18-30 KT DECR 16-24 KT IN
AFT THEN GRADUALLY BCMG E 12-20 KT TONITE-WED.

&&

.FIRE WEATHER...SAHARAN AIR WILL HANG AROUND LONG ENOUGH TO CAP
CONVECTION ALMOST COMPLETELY THIS AFTERNOON. MEANWHILE RELATIVE
HUMIDITY WILL DROP TO LOWER 40S ACROSS LARGE AREA OF SOUTHERN
COAST AND HILLS OF PUERTO RICO ALONG WITH WINDS ALMOST AS HIGH AS
YESTERDAY. FIRE DANGER STATEMENT WAS ISSUED THIS AREA FOR TODAY.

&&

.MARINE...NO CHANGES AS CONDITIONS REMAIN...GENERALLY AT 20 KNOTS
OR LESS AND SEAS NO HIGHER THAN 6 FEET.

&&

.PREV DISCUSSION... /ISSUED 525 AM AST TUE AUG 4 2015/

SYNOPSIS...A MID TO UPPER LEVEL RIDGE WILL PERSIST ACROSS THE
FORECAST AREA THROUGH MID WEEK. RIDGE PATTERN ALOFT WILL THEN
ERODE LATE WEDNESDAY AND THURSDAY AS AN UPPER LEVEL TROUGH
ESTABLISHES ACROSS THE CENTRAL ATLANTIC AND INTO THE NORTHEAST
CARIBBEAN. SURFACE HIGH PRESSURE ACROSS THE CENTRAL ATLANTIC
WILL MAINTAIN MODERATE TO LOCALLY FRESH TRADE WINDS TODAY.

DISCUSSION...CLEAR TO PARTLY CLOUDY SKIES PREVAILED ACROSS
THE LOCAL ISLANDS OVERNIGHT...WITH A FEW SPRINKLES NOTED ACROSS
WINDWARD AREAS. COASTAL TEMPERATURES WERE IN THE UPPER 70S TO
LOW 80S WITH LIGHT AND VARIABLE WINDS.

UNDER LIMITED LOW LEVEL MOISTURE AND RIDGE PATTERN ALOFT...
CONTINUE TO EXPECT A GENERALLY FAIR AND MAINLY STABLE WEATHER
PATTERN ACROSS THE AREA THROUGH WEDNESDAY MORNING. ALTHOUGH
LOCALLY INDUCED AFTERNOON SHOWERS WILL REMAIN POSSIBLE. SOME
HAZINESS IS ALSO EXPECTED TODAY UNDER A WEAK SAL.

AS RIDGE ALOFT ERODES AND AN UPPER LEVEL TROUGH ESTABLISHES
ACROSS THE CENTRAL ATLANTIC AND INTO THE NORTHEAST CARIBBEAN...
A SLIGHT INCREASE IN LOW MOISTURE IS EXPECTED. IN FACT...LATEST
GUIDANCE SUGGESTED PRECIPITABLE WATER NEAR NORMAL VALUES BY THE
END OF THE WEEK WITH A TROPICAL WAVE PASSAGE ON FRIDAY. THIS WILL
RESULT IN A BETTER CHANCE OF TRADE WIND SHOWERS ACROSS WINDWARD
AREAS DURING THE EARLY MORNING HOURS FOLLOWED BY AFTERNOON
CONVECTION OVER THE INTERIOR AND WESTERN SECTIONS OF PUERTO RICO
WEDNESDAY THRU THE UPCOMING WEEKEND.

AVIATION...MOSTLY VFR CONDITIONS ARE EXPECTED ACROSS THE LOCAL
TAF SITES THROUGH THE FORECAST PERIOD. ONLY VERY BRIEF -SHRA ARE
EXPECTED THROUGH 04/18Z. SLIGHT CHANCE OF SHRA/TSRA AROUND TJMZ
AFTER 04/18Z. WINDS FROM THE EAST AT 15-20KT AND GUSTY AFTER
04/13Z...DIMINISHING AFTER 04/23Z.

MARINE...MODERATE TO LOCALLY FRESH TRADE WINDS EXPECTED TODAY.
SMALL CRAFT OPERATORS SHOULD CONTINUE TO EXERCISE CAUTION ACROSS
MOST OF THE LOCAL WATERS THROUGH TONIGHT. SEAS 4-6 FEET
DECREASING TO 3-5 FEET IN THE NEXT FEW DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  90  79  91  80 /   0  20  20  20
STT  92  78  91  78 /  10  20  20  20

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...NONE.
&&

$$

54/13


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