Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 030254
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1054 PM AST THU JUL 2 2015

.UPDATE...MOSTLY CLEAR SKIES WITH SOME HAZE DUE TO SAHARAN DUST
PREVAILED ACROSS THE LOCAL ISLANDS TONIGHT. ONLY LIGHT AND BRIEF
SHOWERS WERE NOTED MAINLY OVER THE CARIBBEAN WATERS. FOR THE REST
OF THE OVERNIGHT AND EARLY MORNING HOURS OF FRIDAY...NOT MUCH IS
EXPECTED TO CHANGE AS DRY AIR ALOFT WILL CONTINUE OVER THE REGION.
THE LATEST TJSJ UPPER AIR SOUNDING INDICATED BELOW NORMAL
PRECIPITABLE WATER AND VERY DRY AIR BETWEEN 850-700MB. NO CHANGES
MADE TO SHORT TERM GRIDS AS FORECAST IN ON TRACK WITH ONLY
ISOLATED PASSING SHOWERS EXPECTED MAINLY OVER THE CARIBBEAN WATERS
AND FROM THE USVI TO THE EASTERN TIP OF PR.

&&


.AVIATION...VFR CONDITIONS WILL PREVAIL ACROSS ALL TAF SITES OVERNIGHT. LOW
LEVEL WINDS WILL CONTINUE MAINLY EAST AT 10 KTS.

&&

.MARINE...NEAR SHORE BUOYS ACROSS THE ISLANDS ARE INDICATING SEAS
OF 3 TO NEAR 5 FEET AND EAST WINDS AROUND 15 KT WITH GUSTS NEAR
20 KT. SEAS ARE EXPECTED TO INCREASE ACROSS THE OFFSHORE WATERS ON
FRIDAY.

&&

.PREV DISCUSSION... /ISSUED 302 PM AST THU JUL 2 2015/

SYNOPSIS...UPPER LEVEL TROUGH/TUTT WILL LINGER NORTHWEST OF
PUERTO RICO OVER THE NEXT SEVERAL DAYS. SURFACE HIGH PRESSURE
ACROSS THE CENTRAL ATLANTIC WILL REMAIN IN PLACE THROUGH AT LEAST
THE END OF THE WEEK...MAINTAINING BREEZY CONDITIONS ACROSS THE
LOCAL REGION. SAHARAN AIR LAYER WILL KEEP THE ATMOSPHERE OVER THE
ISLANDS FAIRLY DRY AND STABLE THROUGH FRIDAY MORNING. A WEAK
TROPICAL WAVE LOCATED NEAR 59 WEST IS FORECAST TO CROSS THE LOCAL
REGION LATE FRIDAY INTO SATURDAY MORNING...BRINGING A FEW ROUNDS
OF SHOWERS ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS. MORE
SAHARAN DUST IS EXPECTED ON SATURDAY AFTERNOON INTO SUNDAY.

DISCUSSION...SAHARAN AIR LAYER WILL CONTINUE TO PRODUCE HAZY
SKIES AS WELL AS LIMITED SHOWER ACTIVITY OVER THE AREA. THIS
RELATIVELY DRY AND STABLE AIR MASS WILL PREVAIL ACROSS THE ISLANDS
THROUGH EARLY FRIDAY. CONDITIONS WILL BECOME MORE UNSTABLE LATE
FRIDAY WHEN THE AFOREMENTIONED WEAK TROPICAL WAVE PASSES MAINLY
SOUTH OF THE LOCAL ISLANDS. MODEL GUIDANCE SUGGESTS PRECIPITABLE
WATER VALUES NEAR 1.5 INCHES BY FRIDAY NIGHT. ALTHOUGH MOISTURE IS
NEAR NORMAL FOR JULY...THE PROXIMITY OF THE UPPER LEVEL TROUGH/TUTT
WILL INCREASE SOMEWHAT THE CONVECTIVE INSTABILITY ACROSS THE
ISLANDS. AS A RESULT...STILL EXPECTING A FEW ROUNDS OF SHOWERS
CAN BE EXPECTED ACROSS PR/USVI WITH THIS WEAK TROPICAL WAVE.
AEROSOL MODELS INDICATED ADDITIONAL SAHARAN DUST MOVING INTO THE
REGION BY LATE SATURDAY MORNING AND CONTINUE ON SUNDAY. THEREFORE...
LIMITED SHOWER ACTIVITY IS FORECAST FOR MOST OF THE 4TH OF JULY
WEEKEND.

AVIATION...VFR THRU TONITE AS SAHARAN AIR CAUSES ISOLD SHRA TO HAVE
RELATIVELY HIGH CIGS. ISOLD/SCT SHRA THU BUT MOST WL PASS S OF
ISLANDS...WITH OUTSIDE CHC OF MVFR FRI AFT MAINLY AT TJSJ/TJBQ.
WIND FL020-FL180 E 18-35 KT BUT DECR AT NIGHT TO NR 10 KT AT TAF
SITES.

MARINE...BREEZY AND CHOPPY SEAS WILL PREVAIL ACROSS THE REGIONAL
WATERS OVER THROUGH THE END OF THE WEEK. SEAS WILL RANGE BETWEEN
4-6 FEET ACROSS THE NEARSHORE WATERS AND UP TO 7 FEET ACROSS THE
OUTER WATERS. THEREFORE...SMALL CRAFT ADVISORIES WILL REMAIN IN
EFFECT FOR THE OFFSHORE CARIBBEAN WATERS AND MONA PASSAGE THROUGH
AT LEAST SATURDAY AFTERNOON.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  89  78  90 /  10  20  40  40
STT  79  90  79  89 /  20  20  30  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...SMALL CRAFT ADVISORY FROM 5 AM FRIDAY TO 6 PM AST SATURDAY FOR
     ANEGADA PASSAGE SOUTHWARD TO 17N-ATLC WATERS OF PUERTO RICO
     AND USVI FROM 10NM TO 19.5N.

     SMALL CRAFT ADVISORY UNTIL 6 PM AST SATURDAY FOR CARIBBEAN
     WATERS OF PUERTO RICO FROM 10 NM TO 17N-MONA PASSAGE
     SOUTHWARD TO 17N.

&&

$$

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