Area Forecast Discussion
Issued by NWS San Juan, PR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXCA62 TJSJ 290146
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
946 PM AST THU AUG 28 2014

.UPDATE...A BAND OF MOISTURE CONTINUES TO INTERSECT PUERTO RICO
AND THE U.S. VIRGIN ISLANDS AS ANOTHER MOISTURE MASS APPROACHES THE
SOUTHERN BORDER OF THE FORECAST AREA. MIMIC PRODUCT IS THE MOST
INSTRUCTIONAL AS IT SHOWS A VERY RICH AIR MASS JUST TO THE SOUTH
WITH THE AXIS OF THE MOISTURE MOVING SLOWLY TOWARD THE AREA FROM
THE SOUTH. SAHARAN DUST HAS CLEANED UP SIGNIFICANTLY WITH
VISIBILITIES OUTSIDE OF RAIN AREAS APPROACHING 40 PLUS MILES.
LITTLE DUST IS EXPECTED THROUGH THE WEEKEND.

&&

.DISCUSSION...HAVE UPDATED THE FORECAST TO INCLUDE HIGHER POPS
ALTHOUGH MOST MODELS EXPECT LOW LEVEL MOISTURE TO TAPER OFF
OVERNIGHT. PRECIPITABLE WATER HOWEVER INCREASES TO ALMOST 2.1
INCHES IN THE WRF AND OVER 2.0 IN THE GFS. ALSO OF NOTE IS THAT
STRONG DIVERGENCE PASSES OVER THE ISLAND BETWEEN 29/06-12Z. THIS
MAY NOT BE AS INFLUENTIAL AS IT COULD BE OWING TO THE LACK OF
HEATING AT THE SURFACE. FOR NOW WILL MAINTAIN SCATTERED TO
NUMEROUS SHOWERS IN THE EAST AND CENTRAL PUERTO RICO INCLUDING THE
SOUTH COAST...AND ISOLATED ELSEWHERE. SCATTERED SHOWERS IN THE
USVI BUT LOOKS LIKE THEY WILL GET AT LEAST A FEW HUNDREDTHS
EVERYWHERE THERE.

&&

.AVIATION...VFR CONDS WILL CONTINUE FOR THE LOCAL TAF SITES WITH
PASSING SHOWERS OVERNIGHT POSSIBLY CAUSING BRIEF MVFR CONDS.
OVERNIGHT SFC WINDS WILL BE MAINLY LIGHT AND VARIABLE ACROSS PR
WHILE THE USVI/BVI SHOULD HAVE LIGHT EASTERLY WINDS. PREVAILING
CEILINGS MAY DEVELOP ACROSS THE LOCAL AREA TONIGHT GENERALLY AT
FL050 OR ABOVE. AFTER 29/13Z WINDS WILL REMAIN EASTERLY AT AROUND 10
KNOTS WITH AFTERNOON SHRA/TSRA EXPECTED ACROSS THE WESTERN INTERIOR
OF PR...LIKELY AFFECTING AREAS IN AND AROUND TJPS...TJMZ...AND TJBQ.


&&

.MARINE...SEAS ARE SUBSIDING EVERYWHERE EXCEPT JUST NORTH OF THE
FORECAST AREA. SMALL CRAFT ADVISORIES HAVE BEEN LOWERED AND WINDS
WILL ABATE SLOWLY ALLOWING SEAS TO RELAX SOME MORE. ATLANTIC SEAS
WILL DIMINISH THROUGH LABOR DAY WHILE ATLANTIC SEAS WILL FALL
THROUGH SATURDAY. HIGHEST SEAS TEND TO HAVE THE LONGEST PERIODS.
SEAS CLOSEST TO SAINT THOMAS AND VIEQUES HAVE DROPPED THE MOST...WITH
SOME SEAS ACTUALLY LOWER THAN 3 FEET IN PROTECTED AREAS.


&&

.PREV DISCUSSION... /ISSUED 237 PM AST THU AUG 28 2014/

SYNOPSIS...RETROGRESSING TUTT LOW NOW CENTERED JUST NORTHEAST OF
THE US VIRGIN ISLANDS WILL CONTINUE TO SHIFT FURTHER WEST NORTHWEST
DURING THE NEXT FEW DAYS. AT LOW LEVELS...A BROAD SURFACE HIGH
PRESSURE CENTERED OVER THE CENTRAL ATLANTIC AND AN EASTERLY
PERTURBATION/TROPICAL WAVE MOVING ACROSS THE EASTERN
CARIBBEAN...WILL HELP TIGHTEN THE LOCAL PRESSURE GRADIENT AND
INCREASE THE LOCAL TRADE WINDS GENERATING A WINDS SURGE WHICH WILL
MOVE ACROSS AND AFFECT THE FORECAST AREA THE REST OF THIS
AFTERNOON THROUGH TONIGHT. MOISTURE WILL INCREASE FRIDAY THROUGH
SUNDAY.

DISCUSSION...VERY ACTIVE WEATHER WAS OCCURRING OVER THE COASTAL
WATERS SOUTH OF PUERTO RICO THIS MORNING AND EARLY AFTERNOON...AS
EASTERLY PERTURBATION MOVES SOUTH OF THE AREA. MEANWHILE...OVER
THE U.S. VIRGIN ISLANDS...PARTLY SUNNY SKIES PREVAILED. A STREAMER
FROM VIEQUES DEVELOPED...PRODUCING SHOWERS OVER THE EASTERN
SECTION OF PUERTO RICO THIS AFTERNOON. THROUGH 2 PM AST THIS
AFTERNOON...REST OF PUERTO RICO WAS UNDER PARTLY CLOUDY SKIES.
A RETROGRESSING TUTT LOW NORTH OF THE U.S. VIRGIN ISLANDS WILL
CONTINUE TO MOVE WEST AND WILL BE LOCATED NORTHWEST OF THE LOCAL
REGION TOMORROW AFTERNOON. THIS UPPER LOW...IN COMBINATION WITH
THE AFOREMENTIONED EASTERLY PERTURBATION AND DAYTIME HEATING...ARE
EXPECTED TO ENHANCE THE SHOWER AND THUNDERSTORMS DEVELOPMENT
TOMORROW AFTERNOON.

MOISTURE IS FORECAST TO INCREASE BY SATURDAY AND SUNDAY WHICH
WILL INCREASE THE CHANCES FOR SHOWERS AND THUNDERSTORMS ACTIVITY
BOTH DAYS. GFS COMPUTER MODEL INDICATED THETA-E VALUES AT 700MB
WILL INCREASE UP TO 335K WITH PW VALUES REACHING 2.0 INCHES SUNDAY
AFTERNOON. IN THE LONG RANGE...AT THIS TIME..NO SIGNIFICANT WEATHER
EVENTS ARE FORECAST TO AFFECT THE LOCAL REGION.

AVIATION...VFR CONDS WILL CONTINUE FOR ALMOST ALL TAF SITES. TJSJ
28/12Z SOUNDING INDICATED STRONG EASTERLY WINDS OF 20 KTS TO UP TO
AS MUCH AS 40 KNOTS BLO FL150. EXPECT BRIEF SFC WND GUST AT ALL TAF
SITES TIL AROUND 28/22Z. MVFR LIKELY IN AT TJMZ DUE TO SHRA/ISOLD
TSRA AND VCSH NR TJBQ TIL 28/22Z.

MARINE...WINDS WILL CONTINUE TO MAINTAIN HAZARDOUS MARINE
CONDITIONS THROUGH TONIGHT MAINLY ACROSS THE OFFSHORE ATLANTIC AND
CARIBBEAN WATERS. CONDITIONS WILL IMPROVE FRIDAY. HOWEVER..SMALL
CRAFT SHOULD CONTINUE TO EXERCISE CAUTION AS SEAS UP TO 6 FEET AD
WINDS UP TO 18 KNOTS ARE EXPECTED.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  88  77  89 /  50  50  50  50
STT  79  88  77  88 /  40  30  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

25/12







USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.