Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 270159
Area Forecast Discussion
National Weather Service San Juan PR
959 PM AST FRI AUG 26 2016
.UPDATE...Numerous showers and thunderstorms affected the
northwestern and southern sections of PR this afternoon. Rainfall
accumulations between 2 to just over 4 inches of rain were
reported across Ponce and Guanica. A flash flood warning was
issued for Ponce and several flood advisories were also required
for urban and small stream flooding across southwestern PR and NW
PR. A line of showers with possible isolated thunderstorms is
expected to move briefly across the southeastern sections of PR in
the next hour or so. Variably cloudy skies will continue overnight
over the islands. Minor changes made to short term grids to
include tstms. However they should remain mainly across the
offshore Caribbean waters.
.AVIATION...Showers will affect TIST/TISX/TJPS/TJSJ through the
morning hours. Afternoon convection may produce mountain obscuration
across the Cordillera Central. In addition, between 27/17-
27/22z...periods of MVFR conditions with mountain obscurations can
be expected over TJMZ and TJBQ. Low level winds will be mainly
southeast at 10 to 15 kts and locally higher inland around SHRA/TSRA.
.MARINE...Near shore buoys across the islands are indicating seas
under 3 feet and light winds from the east-southeast. Small ENE
swell is expected to fill in across the Atlantic waters and
Anegada Passage by early Saturday morning. No major change from
.PREV DISCUSSION... /issued 156 PM AST FRI AUG 26 2016/
SYNOPSIS...The presence of tropical storm Gaston well northeast
of the region across the Central atlantic...and the broad area of
low pressure with associated tropical wave extending across the
western caribbean and the windward passage, will continue to induce
a fairly moist southeast wind flow across the region today and into
the upcoming weekend. Weak high pressure ridge aloft will continue
to shift westward over the next few days as a tutt low and associated
trough will retrogress west southwest and reach the Northeastern
Caribbean late Saturday into Sunday.
DISCUSSION...The moist southeasterly wind flow and weak upper
level diffluence across the area will continue to aid in the
formation of showers and isolated thunderstorms across the region
during the afternoon and early evening hours. Activity should
then diminish over land during the late evening, leaving variably
cloudy to partly cloudy skies. However...by early morning, expect
a light to moderate southeast wind flow to bring periods of passing
showers to east and southeast portions of the islands. Some showers
may produce moderate to locally heavy rainfall, but will be of short
duration. On Saturday afternoon... available moisture along with local
and diurnal effects will give way to showers and isolated thunderstorm
development across parts of the central and west to northwest sections
of Puerto Rico. Brief periods of passing showers can be expected mainly
over the west end of the U.S Virgin Islands steered by the prevailing
southeast wind flow.
For the rest of the weekend and into Monday of next week...tutt induced
low level trough will move across the area in tandem with tutt low which
is forecast to move across the Northeastern Caribbean by Sunday. This
along with the still fairly moist southeast wind flow will give way
to additional showers and isolated thunderstorms. Some of the activity
will be locally enhanced across parts of the interior and northern
half of PR including parts of the San Juan metro area. Conditions will
gradually improve by Tuesday of next week as moisture convergence across
the region gradually more easterly in response to high pressure building
north of the region.
AVIATION...MVFR conds likely at TJBQ the rest of the afternoon.
TJMZ...TJSJ and TJPS will experience VCTS at times between 17Z-21Z.
Mountain obscurations will continue across the Cordillera Central
until at least 22Z. Elsewhere...VFR conds expected with -SHRA from
time to time. SE winds of 15-25 kt will prevail below FL100.
MARINE...Seas of 3-5 feet will continue overnight through Saturday.
For the rest of the weekend...a small ENE swell of 3-4 feet generated
by Hurricane Gaston will reach the local Atlantic waters and Caribbean
waters. No small craft advisories are anticipated over the next
.PRELIMINARY POINT TEMPS/POPS...
SJU 80 91 80 91 / 40 30 20 40
STT 80 90 80 90 / 40 30 40 40