Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 240904
Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Mon Apr 24 2017
.SYNOPSIS...Moist and unstable conditions will keep the potential
for showers and a few thunderstorms high through at least Tuesday.
Conditions will gradually improve by midweek as mid level ridge
builds over the Central Caribbean.
.SHORT TERM...Today through Wednesday...Surface low pressure across
the southwestern Atlantic and a surface high pressure northeast of
the area are promoting low level wind convergence and favoring a
moist southeasterly wind flow across the region. Precipitable water
is expected to remain above 2 inches across much of the forecast
area. Deep trof aloft is forecast to move from the west through
Wednesday. Providing good divergence aloft to enhance the
development of thunderstorm with periods of heavy rainfall.
For today, shower activity should continue to increase across the
USVI`s and the southeastern/interior sections of PR through the rest
of the morning hours. Hi-res models continue to suggest best shower
activity and possible isolated thunderstorm development over the
eastern half of PR into the USVI`s later this afternoon into the
evening hours. As trof aloft moves near the region on Tuesday,
organized convection and higher rainfall amounts are expected on
Tuesday afternoon, mainly over and to the north of the Cordillera
Central as well as across the USVI`s. On Wednesday, the base of the
trof should move to the northeast of the forecast area as ridge
builds from the west. However, sufficient moisture will linger
across the islands to aid the development of diurnally induced
afternoon showers over the islands.
Residents across the islands should continue to monitor the progress
of the weather conditions as periods of frequent rainfall can result
in urban and small stream flooding as well as localized flash
.LONG TERM...Thursday through Tuesday...Overall moisture content
will decrease through Saturday as a mid-upper level ridge will
develop over the Western and Central Caribbean. Easterly winds
will return to the local area on Thursday as a strong high pressure
builds over the Central Atlantic. Weather conditions will remain
fairly stable from Thursday through the weekend as subsidence and
drier air aloft will limit the shower coverage across the local
An upper level trough/TUTT will amplify over the Tropical Atlantic...
northeast of the region by early next week. As the TUTT retrogress
across the Northeast Caribbean Islands...weather conditions will
become unstable between Tuesday and Wednesday next week.
.AVIATION...BKN-OVC cigs between FL040-FL090 will continue
across the forecast area with mtn top obscd across mainland PR.
Brief MVFR at times possible across much of the terminals today as
cloudiness and TSRA/SHRA increases over the waters and between the
Leeward/USVI/Eastern PR terminals during the afternoon/evening
hours. Southeast winds below FL050 will continue at 10-22
knots...westerlies abv and increasing w/height.
.MARINE...Prevailing winds will shift to the south-southeast over
the next few days as a surface low moves over the Western Atlantic.
A decaying northerly swell of 5-7 feet will subside through tonight.
Hazardous marine conditions will continue across the Offshore Waters
and Caribbean Passages through late tonight. A high risk of rip
currents remains in effect for the Atlantic Beaches of Puerto Rico
.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 89 76 / 40 40 50 50
STT 85 77 84 76 / 60 60 60 60
PR...High Rip Current Risk through late tonight for Culebra-North
Central-Northeast-Northwest-San Juan and Vicinity-Southeast-
AM...Small Craft Advisory until 8 PM AST this evening for Anegada
Passage Southward to 17N-Caribbean Waters of Puerto Rico
from 10 NM to 17N-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 AM AST Tuesday for Atlantic Waters
of Puerto Rico and USVI from 10 NM to 19.5N.
Small Craft Advisory until 8 AM AST this morning for Coastal
Waters of Southern USVI Vieques and Eastern Puerto Rico out