Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 021456
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1056 AM AST THU JUL 2 2015

.DISCUSSION...DEEP LAYER OF SAHARAN AIR EVIDENT ON 12Z TJSJ AND
MACM SOUNDINGS 5-15 KFT WITH A SLIGHTLY STRONGER LOW LEVEL JET
JUST BELOW IT THAN GFS EXPECTED...PEAKING AT 28-30 KT. RADAR
SUGGESTS THAT JET IS BEGINNING TO MIX DOWNARD WHICH WILL KEEP LAND
SURFACES BREEZY. SUBSTANTIAL INVERSION AT THE BASE OF THE SAHARAN
AIR WOULD REQUIRE SURFACE TEMPERATURES TO REACH WELL INTO THE 90S
TO INITIATE CONVECTION ON LOWER ELEVATIONS THOUGH ISOLATED SHOWERS
ARE POSSIBLE FOR INTERIOR AND WEST PR THIS AFTERNOON DUE THE
ELEVATED HEAT SOURCE.

WILL NOT MAKE CHANGES TO FORECASTS/GRIDS AS THEY SHOW APPROPRIATE
DRYNESS AND BREEZES. DEVELOPING CLOUDS AS WE HAVE NOW WILL LIMIT
HEATING A LITTLE.

&&

.AVIATION...VFR THRU AT LEAST TONITE AS SAHARAN AIR WILL CAUSE
EVEN MOST OF THE ISOLD SHRA TO HAVE RELATIVELY HIGH CIGS. WIND TO
GUST CLOSE TO 30 KT SOME LOCATIONS THIS AFTERNOON...MOSTLY LIKELY
AT TJBQ/TJSJ/TISX.

&&

.MARINE...MODERATE TO FRESH BREEZES TO CONTINUE TODAY AND DO NOT
BELIEVE THE LOW LEVEL JET WILL KICK SUSTAINED WINDS TO HIGHER
THAN THE 21 KNOTS SHOWN IN GRIDS THOUGH SOME GUSTS WILL REACH 30
KNOTS. WILL ADJUST GUSTS UPWARD SOMEWHAT. NO ADJUSTMENT IN SEAS.

&&

.PREV DISCUSSION... /ISSUED 538 AM AST THU JUL 2 2015/

SYNOPSIS...AT UPPER LEVELS...A WEAK LOW ALONG 70 NORTH NORTH OF
THE DOMINICAN REPUBLIC WILL SHIFT NORTH ON FRIDAY AND REMAIN ABOUT
500 MILES NORTH OF THE DOMINICAN REPUBLIC UNTIL NEXT THURSDAY.
FLOW OVER THE AREA WILL REMAIN SOUTHWEST UNTIL MONDAY WHILE
WEAKENING.

AT MID LEVELS...HIGH PRESSURE IN THE CENTRAL ATLANTIC WILL SHIFT
TO NORTH OF THE AREA BY MID WEEK NEXT WEEK. MID LEVELS WILL REMAIN
MOSTLY DRY.

AT LOWER LEVELS... A WEAK TROPICAL WAVE WILL MOVE THROUGH THE AREA
FRIDAY EVENING BRINGING SOME MOISTURE...SHOWERS AND POSSIBLY
THUNDERSTORMS WITH IT. CONDITIONS BECOME DRY AGAIN ON SUNDAY. HIGH
PRESSURE CONTINUES IN THE CENTRAL ATLANTIC THROUGH MID WEEK NEXT
WEEK...THEN IT RETREATS INTO THE EASTERN ATLANTIC LEAVING ONLY A
WEAK RIDGE ACROSS THE ATLANTIC INTO FLORIDA. THIS WILL ALLOW TRADE
WINDS TO WEAKEN SOMEWHAT LATE NEXT WEEK.

DISCUSSION...VERY SMALL AND RELATIVELY LIGHT SHOWERS WERE SEEN
OVER THE ATLANTIC AND CARIBBEAN WATERS BUT VERY FEW MADE IT OVER
LAND IN EITHER PUERTO RICO OR THE U.S. VIRGIN ISLANDS THIS
MORNING AND NO MEASURABLE RAINFALL WAS OBSERVED. MOSTLY DRY
CONDITIONS WILL PREVAIL THROUGH FRIDAY MORNING...ALTHOUGH A FEW
ISOLATED SHOWERS OR THUNDERSTORMS ARE POSSIBLE IN WESTERN AND
INTERIOR PUERTO RICO THIS AFTERNOON AND FRIDAY AFTERNOON. SOME
SAHARAN DUST IS ALSO EXPECTED TO MOVE INTO THE AREA TODAY BRINGING
REINFORCEMENT TO THE DRIER AIR NOW IN PLACE. ON FRIDAY EVENING A
TROPICAL WAVE WILL MOVE ACROSS THE AREA WITH SOME BETTER MOISTURE
BEHIND IT...BUT AMOUNTS ARE EXPECTED TO BE LIGHT AND LIGHTER THAN
BROUGHT BY THE WAVE THAT PASSED THROUGH TUESDAY INTO WEDNESDAY
THIS WEEK. MOISTURE WILL DIMINISH EVEN BELOW PRESENT LEVELS ON
SUNDAY. BY MONDAY MOISTURE WILL INCREASE AND ON TUESDAY
PRECIPITABLE WATER SHOULD EXCEED 1.9 INCHES IF ONLY FOR A FEW
HOURS IN THE AFTERNOON. HENCE DURING THE NEXT 7 DAYS ONLY LIMITED
SHOWER ACTIVITY CAN BE EXPECTED. THE MOISTURE ON MONDAY WILL COME
FROM THE NORTHEAST AND IS NOT ACTUALLY ASSOCIATED WITH THE
TROPICAL WAVE TO ARRIVE ON TUESDAY SO IT IS EXPECTED TO AFFECT
NORTHEAST PUERTO RICO MORE. AS IT IS A NARROW PULSE THE GFS IS
INDICATING LITTLE ADDITIONAL MOISTURE FOR THE NORTHERN U.S.
VIRGIN ISLANDS THEN...BUT SOME MOISTURE FOR TUESDAY THERE.

AVIATION...MAINLY VFR CONDITIONS EXPECTED ACROSS ALL TERMINALS THRU
THE FCST PERIOD. HAZY SKIES EXPECTED DUE TO SAHARAN DUST BUT VSBY
SHOULD REMAIN P6SM. DURING THE AFTERNOON HRS SHOWERS AND CLOUDINESS
MAY FORM MAINLY OVER THE INTERIOR AND WESTERN PR. SFC EAST WINDS 10-
15 KT EARLY IN THE MORNING...INCREASING AT 15 TO 25 KT WITH HIGHER
GUSTS AFTER 02/12Z.

MARINE...SEAS UP TO 7 FEET ARE EXPECTED IN THE SOUTHWEST PORTION
OF THE MONA CHANNEL AND CARIBBEAN LOCAL OUTER WATERS. SEAS WILL
INCREASE OVER THE AREA TONIGHT AND FRIDAY SUCH THAT SMALL CRAFT
ADVISORIES WILL BE NEEDED IN ALL OUTER WATERS AND PASSAGES BY
EARLY FRIDAY MORNING. CONDITIONS ARE EXPECTED TO BEGIN TO SUBSIDE
AFTER SUNDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  79  89  78 /   0  10  20  40
STT  90  79  90  79 /  10  20  20  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...HIGH RIP CURRENT RISK UNTIL 6 PM AST THIS EVENING FOR ST CROIX.

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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