Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 250917
Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Sat Mar 25 2017
.SYNOPSIS...Deep layered moisture and trof pattern aloft will
maintain an unsettled weather pattern through the rest of the
weekend. A surface trough and a developing low to the north of
Hispaniola and the Mona Passage will continue to promote a
moderate southerly wind flow over the forecast area. At least
through the weekend the potential for urban and small stream
flooding will remain high across the islands. The low and a
building high across the Western Atlantic will promote northwest
to northerly winds by early next week.
.SHORT TERM...Today through Monday...
A shear line across the Atlantic waters in combination with a
developing low pressure system just north of Puerto Rico will
maintain a very moist and unstable southwest wind flow across the
region until at least Sunday. At the same time an upper level trough
extending from the central Caribbean northward across Jamaica and
Cuba and then over the Atlantic waters has maintained an associated
jet over the Atlantic waters to the north of the region. These
features will aid in the development of showers and thunderstorms
across the region today an until early the upcoming week. Abundant
tropical moisture embedded in the wind flow will continue to bring
showers and thunderstorms across the Caribbean waters and then
across Puerto Rico and the U.S. Virgin Islands today.
Early this morning Doppler radar indicated scattered to numerous
showers moving from the Caribbean waters, north northeastward
across south central and eastern sections of Puerto Rico as well
across Vieques, Culebra and the U.S. Virgin Islands. Urban and
small stream flooding are possible today and Sunday across Puerto
Rico and the U.S. Virgin Islands. Drier air will filter across the
region on Monday, but moisture will linger across the region to
produce some showers especially during the afternoon hours.
.LONG TERM...Tuesday Through Saturday...
Surface low is forecast to move north of the islands through early
next week across the Central Atlantic as a building ridge across
the Western Atlantic builds and moves north of the islands by
late in the week. This will result in a northwest to northerly
wind flow through the middle of the week. As the low pulls away,
moisture content is expected to diminish quickly over the islands
but moisture content will remain high over the Caribbean Sea. At
the moment, best chance for showers are expected between
eastern PR and the USVI on Tuesday. At upper levels another short
wave trof is expected to move on Wednesday. Then a ridge will
build across the Caribbean basin. This in combination with a cool
northerly wind flow due to the surface high will promote drier air
and seasonable weather conditions across the islands.
.AVIATION...SHRA/TSRA will produce periods of MVFR or even IFR
conditions across the Leewards, USVI, TJPS and TJSJ taf sites until
at least 25/16z. VCSH expected across the rest of the local flying
area this morning. Mountain obscurations will continue over PR thru
26/00Z. Bands of moisture with embedded +RA and TSRA will move
occasionally over the local flying area this afternoon to produce
periods of MVFR conditions across most taf sites.
.MARINE...A large northerly swell will fill in across the local
passages and Atlantic waters through Sunday. Small craft
advisories are in effect. Seas should range between 8-10 feet
across the offshore Atlantic and under 8 feet elsewhere across the
passages and the northern coastal waters of the islands. A high
surf advisory is in effect for the northwest through northeast
coast of PR and a high rip current risk is also in effect for the
same areas including northern Culebra and northwest St. Thomas.
Beach goers are urged to avoid these coastal areas through the
rest of the weekend.
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 75 / 50 20 50 40
STT 81 74 82 75 / 20 50 50 50
PR...High Rip Current Risk through Sunday afternoon for Culebra-
Mayaguez and Vicinity-North Central-Northeast-Northwest-San
Juan and Vicinity-Southeast-Western Interior.
High Surf Advisory until 6 AM AST Sunday for Mayaguez and
Vicinity-North Central-Northeast-Northwest-San Juan and
VI...High Rip Current Risk through Sunday afternoon for
St.Thomas...St. John...and Adjacent Islands.
AM...High Rip Current Risk through Sunday afternoon for Coastal
Waters of Northern USVI and Culebra out 10 NM-Coastal
Waters of Southern USVI Vieques and Eastern Puerto Rico out
Small Craft Advisory from 8 AM this morning to 8 AM AST Sunday
for Coastal Waters OF Northwestern Puerto Rico out 10 NM-
Coastal Waters of Northern Puerto Rico out 10 NM-Coastal
Waters of Northern USVI and Culebra out 10 NM-Mona Passage
Southward to 17N.
Small Craft Advisory until 2 PM AST Sunday for Atlantic Waters
of Puerto Rico and USVI from 10 NM to 19.5N.
Small Craft Advisory from 2 PM this afternoon to 8 AM AST Sunday
for Anegada Passage Southward to 17N.