Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 010253
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1053 PM AST SAT JAN 31 2015

.UPDATE...LOW TO MID LEVEL MOISTURE CONVERGENCE AIDING IN THE
DEVELOPMENT OF SHOWERS ACROSS THE REGIONAL WATERS AND ALONG THE
NORTH COASTAL AREAS OF PUERTO RICO...AS WELL AS OVER THE U.S.VIRGIN
ISLANDS. THIS COMBINED WITH THE GRADUAL TIGHTENING OF THE LOCAL PRESSURE
GRADIENT IN RESPONSE TO SURFACE HIGH PRESSURE BUILDING ACROSS THE
WESTERN ATLANTIC AND NORTH OF THE REGION...WILL ENHANCE THE NORTHEASTERLY
TRADE WINDS OVERNIGHT THROUGH SUNDAY...RESULTING IN THE DEVELOPMENT
OF OVERNIGHT AND EARLY MORNING PASSING SHOWERS. ON SUNDAY...THE LOW
LEVEL MOISTURE CONVERGENCE ALONG WITH LOCAL AND DIURNAL EFFECTS WILL
LEAD TO SOME SHOWER DEVELOPMENT. ACTIVITY HOWEVER SHOULD BE LIMITED
AND LESSER ENHANCED AS THE UPPER TROUGH AND ASSOCIATED JET SEGMENT
SHOULD PULL FURTHER EAST OF THE REGION AND ALLOW FOR WEAK UPPER
LEVEL RIDGING AND INCREASING SUBSIDENCE. DUE TO THE PREVAILING
NORTHEASTERLY WIND FLOW...EXPECT AFTERNOON SHOWER DEVELOPMENT TO
BE FOCUSED ACROSS THE CENTRAL INTERIOR AND SOUTHWEST SECTIONS OF
PUERTO RICO. NO SIGNIFICANT CHANGES MADE TO THE INHERITED FORECAST
PACKAGE AT THIS TIME AS IT HAD GOOD HANDLE ON THE PRESENT AND EXPECTED
CONDITIONS FOR THE NEXT FEW DAYS.

&&

.AVIATION UPDATE...BRIEF PERIODS OF MVFR CIGS POSSIBLE IN PASSING SHRA
ACROSS TJBQ AND TJSJ OVERNIGHT AND SUN MORNING. VFR CONDS EXPECTED
ELSEWHERE. THEN...AFTERNOON SHRA WILL DEVELOP OVER THE INTERIOR...
WEST AND SOUTH PR BETWEEN 18Z-22Z. THEREFORE...MVFR/IFR CONDS CAN BE
EXPECTED IN AND AROUND TJMZ AND TJPS. MOUNTAIN OBSCURATIONS ARE
LIKELY SUN AFTERNOON ACROSS THE WESTERN INTERIOR PR. NE WINDS OF
10-20 KT WILL PREVAILED BELOW FL150.

&&

.MARINE UPDATE...NORTHERLY SWELLS WILL INVADE AND GRADUALLY SPREAD
ACROSS THE ATLANTIC WATERS AND LOCAL PASSAGES DURING THE REST OF THE
WEEKEND AND INTO EARLY NEXT WEEK. THIS ALONG WITH THE INCREASING TRADE
WINDS WILL LEAD TO CHOPPY AND HAZARDOUS SEAS ACROSS THE OFFSHORE ATLANTIC
WATERS OVERNIGHT AND THE MONA PASSAGE BY SUNDAY AFTERNOON. BY MONDAY
AND TUESDAY...THE INCREASING NORTHERLY SWELL ACTION AND ROUGH SEAS
WILL INCREASE THE RISK OF DANGEROUS RIP CURRENTS AS WELL AS DETERIORATING
SURF ZONE CONDITIONS. PLEASE REFER TO THE LATEST COASTAL WATERS FORECAST
AND MARINE WEATHER STATEMENT ISSUED BY THE NATIONAL WEATHER SERVICE
WFO SAN JUAN PR.

&&

.PREV DISCUSSION... /ISSUED 241 PM AST SAT JAN 31 2015/

SYNOPSIS...MID TO UPPER LEVEL TROUGH ENTERING THE WESTERN
ATLANTIC WILL MOVE OVER THE OPEN ATLANTIC WATERS THROUGH THE
WEEKEND. AVAILABLE MOISTURE WILL LINGER ACROSS THE REGION FOR THE
NEXT FEW DAYS. SURFACE HIGH PRESSURE BUILDS TO THE NORTH OF THE
LOCAL AREA EARLY NEXT WEEK...TIGHTENING THE LOCAL PRESSURE
GRADIENT.

DISCUSSION...CLOUDINESS WITH SHOWERS WERE OBSERVED THIS MORNING
MAINLY OVER THE COASTAL WATERS NORTH OF THE LOCAL ISLANDS. EARLY
IN THE AFTERNOON...SHOWERS BEGAN TO DEVELOP OVER THE CORDILLERA
CENTRAL OF PUERTO RICO. THESE SHOWERS WERE GENERALLY MOVING WEST
AT 10 TO 15 MPH. AVAILABLE MOISTURE...COMBINED WITH DAYTIME
HEATING AND OROGRAPHIC EFFECTS WERE RESPONSIBLE FOR THIS SHOWER
ACTIVITY. FOR TONIGHT...MOISTURE IS EXPECTED TO INCREASE A LITTLE
BIT...WHICH WILL ENHANCE THE CHANCE FOR SHOWERS MAINLY ALONG THE
NORTH COAST OF PUERTO RICO AND THE NORTHERN U.S. VIRGIN ISLANDS.

FOR THE REST OF THE WEEKEND THROUGH EARLY NEXT WEEK...AVAILABLE
MOISTURE WILL LINGER ACROSS THE REGION. SURFACE HIGH PRESSURE
BUILDS TO THE NORTH OF THE LOCAL AREA EARLY NEXT WEEK...TIGHTENING
THE LOCAL PRESSURE GRADIENT. THEREFORE...WINDS WILL INCREASE
SOMEWHAT THROUGH MID WEEK. IN GENERAL..IN THE LONG TERM...NO
SIGNIFICANT WEATHER EVENTS ARE FORECAST TO AFFECT THE LOCAL
REGION.

AVIATION...ONLY BRIEF PERIODS OF MVFR CONDITIONS ARE EXPECTED
ACROSS TJSJ...TJMZ AND TJBQ WITH VCSH POSSIBLE IN AND AROUND TIST
AND TISX UNTIL 31/22Z. AFTER 22Z...MOSTLY VFR CONDITIONS EXPECTED
ACROSS MOST OF THE LOCAL FLYING AREA. LATEST TJSJ SOUNDING INDICATED
AN EAST TO EAST NORTHEAST LOW LEVEL WIND FLOW UP TO 15 KNOTS FROM
THE SURFACE TO 10K FEET...BECOMING WESTERLY AND VERY STRONG ABOVE
20K FEET.

MARINE...SMALL CRAFT ADVISORIES WILL BE IN EFFECT LATE TONIGHT
FOR THE OFFSHORE ATLANTIC WATERS. SEAS UP TO 7 FEET AND WINDS UP TO
20 KNOTS ARE EXPECTED.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  74  81  73  86 /  50  50  40  40
STT  73  83  75  84 /  50  50  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 6 PM AST TUESDAY FOR ATLC WATERS OF
     PUERTO RICO AND USVI FROM 10NM TO 19.5N.

     SMALL CRAFT ADVISORY FROM 6 PM SUNDAY TO 6 AM AST TUESDAY FOR
     MONA PASSAGE SOUTHWARD TO 17N.

&&

$$

11/09





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