Area Forecast Discussion
Issued by NWS San Juan, PR

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802
FXCA62 TJSJ 221324
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
924 AM AST FRI MAY 22 2015

.DISCUSSION...NO CHANGES MADE TO FORECAST AT THIS TIME...
INHERITED FORECAST PACKAGE LOOKS GOOD FOR NOW. PRESENT WEATHER
CONDITIONS AND LATEST MODEL FORECAST GUIDANCE...ALONG WITH RECENT
TJSJ 22/12Z UPPER AIR SOUNDING DATA....CONTINUED TO SUGGEST
VERY SHALLOW MOISTURE BELOW 850 MILLIBARS WITH DRY AND STABLE
SAHARAN AIR LAYER SPREADING ACROSS THE REGION. LAYERED PWAT WAS
AROUND 1.91 INCHES BUT MOSTLY MID TO HIGH LEVEL CLOUDS SPREADING
ACROSS THE REGION UNDER THE DOMINANT WESTERLIES ALOFT.

&&

.AVIATION UPDATE...BKN-OVC MID TO HIGH LVL CLDS STREAMING
EASTWARDS ACROSS THE FLYING AREA. FEW L/LVL CLDS BTW FL020-050
WITH NO SIG BUILDUPS...SLGHT HZ ALOFT DUE TO SUSPENDED SAHARAN
DUST PARTICULATES SPREADING WESTWARDS ACROSS THE EASTERN
CARIBBEAN. NO OTHER CHG TO PREVIOUS FCST DISCUSSION.

&&

.MARINE...LATEST DATA FROM SURROUNDING BUOYS AND RECENT OBSERVATIONS
CONTINUE TO SUGGEST FAIRLY TRANQUIL SEAS OF 4 FEET OR LESS AND
WINDS 15 KNOTS OR LESS WILL PREVAIL DURING THE REST OF THE DAY.

&&

.PREV DISCUSSION... /ISSUED 544 AM AST FRI MAY 22 2015/

SYNOPSIS...LOCAL REGION LIES BETWEEN AN UPPER LEVEL LOW TO THE
NORTH AND A SUBEQUATORIAL RIDGE TO THE SOUTH. THIS UPPER LEVEL
FEATURES HAVE CAUSED THE SUB-TROPICAL JET TO MODULATE OVER THE
LOCAL ISLANDS SINCE EARLY THIS WEEK. MID LEVEL DRY AIR WITH
SAHARAN DUST PARTICLES WILL GRADUALLY SPREAD OVER THE REGION
TODAY AND CONTINUE DURING THE WEEKEND. THIS WILL RESULT HAZY SKIES
AND LIMITED SHOWER ACTIVITY OVER THE NEXT FEW DAYS.

DISCUSSION...HIGH CLOUDS HAVE MAINTAINED THE LOCAL AREA UNDER
MOSTLY CLOUDY SINCE MIDNIGHT. RADAR OBS SHOWED MOST OF SHOWERS
AFFECTING THE OFFSHORE ATLANTIC WATERS...WITH LITTLE OR NO RAINFALL
OBSERVED OVER LAND AREAS. THE NASA/CIRA LAYER PRECIPITABLE WATER
ANALYSIS BETWEEN 850MB-700MB IS SUGGESTING THAT THE SAHARAN AIR
LAYER HAVE ENTERED INTO THE EASTERN CARIBBEAN. AS THE DAY PROGRESSES...
THIS SAHARAN AIR LAYER WILL SPREAD OVER PR/USVI RESULTING IN HAZY
SKIES AND LOWER VISIBILITIES. THIS DRY AND HOT AIR MASS WILL STRENGTHEN
THE SUBSIDENCE INVERSION ACROSS THE NORTHEAST CARIBBEAN ISLANDS...
SUPPRESSING THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS
THE LOCAL AREA. HI-RES MODEL GUIDANCE ONLY SUGGEST A FEW ISOLATED
SHOWERS OVER NW PUERTO RICO THIS AFTERNOON. THIS DRY PATTERN IS
FORECAST TO CONTINUE THROUGH THE UPCOMING WEEKEND.

FOR EARLY NEXT WEEK...MOISTURE RETURN TO NORMAL LEVELS AND TYPICAL
TRADE WIND PATTERN WILL ESTABLISH ONCE AGAIN ACROSS THE ISLANDS.
BY THE END OF NEXT WEEK...SOME OPERATIONAL MODELS ARE SUGGESTING
MORE ORGANIZED CONVECTION ACROSS THE NORTHEAST CARIBBEAN REGION.

AVIATION...AIR HAS TURNED QUITE DRY FL050 TO FL200 OVR PR/USVI WI
HIER MOISTURE AND SHRA/ISOLD TSRA CONT THIS MORNING FM HISPANIOLA TO
N OF PR ALG 20N. VFR PR/USVI XCPT LCL MVFR IN SHRA/ISOLD TSRA
XPCTD FRI/SAT AFT WESTERN PR...FEW OBSCD MTN. ISOLD SHRA ELSEWHERE
THRU TONITE. WIND SE 10-20 KT BCMG E 15-25 KT BY 12Z SAT.

MARINE...WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA
FOR ALL WATERS INTO NEXT WEEK. FOR TODAY...EXPECT WINDS AROUND 15 KNOTS
AND SEAS OF 2-4 FEET. A SLIGHT INCREASE IN THE EASTERLY TRADE WINDS
EXPECTED DURING THE WEEKEND. THIS MAY INCREASE THE SEAS UP TO 5 FEET
ACROSS THE OFFSHORE WATERS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  91  79  89  78 /  20  10  20  20
STT  88  79  88  77 /  20  20  20  20

&&

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

$$

09/27



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