Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 251515
Area Forecast Discussion
National Weather Service San Juan PR
1115 AM AST Tue Apr 25 2017
.UPDATE...Light to briefly moderate showers were observed in the
morning hours across portions of eastern and southern PR as well
as across the USVI, leaving minimal amounts of rain. This is due
to the southeasterly wind flow and the available moisture. Because
the inherited forecast did not have showers across south central
PR we decided to make a minor adjustment to account for the latest
observations and expected weather for the rest of the morning.
Satellite imagery indicates that cloudiness already started
developing across a few areas of the NW quadrant of PR, which is
expected to eventually be the area with heaviest showers and
potential thunderstorms. The rest of PR and across the northern
USVI we still expect scattered showers and isolated thunderstorms
for the afternoon hours. The latest guidance is still in agreement
with the rest of the inherited forecast, so no changes were made
except for the morning hours.
.AVIATION...No changes from previous discussion, VFR conds
expected across the local terminals. VCSH expected today across
most of the local terminals but VCTS possible in the afternoon
across TJSJ, TJBQ, and TJMZ. SE Winds at 10-15KT with sea breeze
variations, becoming slightly lighter after 26/00Z.
.MARINE...Small craft should exercise caution as seas will be up
to 6 feet and winds up to 20 knots today. High risk of rip
currents continue for the beaches of northeastern and north
central PR as well as the island of Culebra. Rip current risk
becoming moderate for tonight and tomorrow.
.PREV DISCUSSION... /issued 510 AM AST Tue Apr 25 2017/
SYNOPSIS...Trough aloft moves over the area from the west today.
Zonal flow follows with ridge building across the Western
Caribbean and TUTT low developing northeast of the area by late
in the weekend into early next week. At lower levels, broad ridge
pattern is to persist across the North Central Atlantic through
the rest of the week and a surface low will move north across the
mid Atlantic coast of the USA during the next few days. Moist
southeasterly winds will continue today.
SHORT TERM....Tuesday through Thursday...
Variably cloudy skies prevailed overnight and early this morning
across the local islands. Passing showers were observed across the
waters as well as eastern Puerto Rico and the U.S. Virgin
Islands. However, rainfall accumulations associated with these
showers were minimal. Coastal temperatures were in the upper 70s
to low 80s under southeasterly winds at 10 knots or less.
Ridge aloft will continue to erode as a broad mid to upper level
trough moves across the western Atlantic and over the local islands.
The jet maxima associated with the aforementioned trough will favor
a divergent pattern, particularly today. Trofiness is then expected
to move away on Wednesday with a second trough developing north of
the area Friday and into the upcoming weekend. At lower levels, a
surface low across the western Atlantic and a surface high across
the central Atlantic will continue to promote a moist southeasterly
wind flow during the next two days or so. Although easterly winds
will return to the forecast area Thursday, moisture advection will
persist across the forecast area.
Therefore, expect a few passing showers across USVI and E PR during
the morning hours with shower and thunder activity increasing
across the forecast area in the afternoon. These showers and
thunderstorms are expected mainly east and north of the Cordillera
Central as well as USVI. With the heaviest showers and thunderstorms
urban flooding is likely. As the trough moves away early Wednesday,
expect another round of overnight and early morning showers with
thunderstorms possible across USVI and E PR. Wednesday afternoon and
into Thursday, a more seasonable weather pattern is expected with
locally induced showers across west PR in the afternoon.
LONG TERM...Friday through Wednesday...
Fair weather conditions are expected to prevail. Surface high
pressure builds further to the west and north of the area. Winds
expected to increase from the east-northeast. Trade wind shower
pattern and limited afternoon shower activity confined to the
interior and southwest quadrant of PR is expected as well as
streamers developing off the USVI`s. A TUTT low is forecast to
develop northeast of the region by early next week. As the TUTT
retrogress across the Northeast Caribbean Islands...weather
conditions will become unstable by midweek next week.
AVIATION...Mostly VFR conds expected this morning at all TAF sites
with -SHRA possible at the Leeward and USVI terminals as well as
JSJ. SHRA/TSRA development expected aft 25/16z and this may result
in MVFR or even IFR conds in and around JSJ and JBQ through 25/22z.
Southeasterly winds at 10 to 15 knots with sea breeze variations,
becoming light and variable overnight.
MARINE...Northerly swell will subside today across the Atlantic
waters. Small crafts should exercise caution due to seas up to 6
feet across the offshore Atlantic waters and due to southeasterly
winds up to 20 knots across much of the Caribbean waters and
passages. There is a moderate to high risk of rip currents for the
northern beaches of PR and Culebra. Moderate risk elsewhere
across the rest of the islands. Seas under 5 feet are expected
from Wednesday through the weekend. East winds will prevail after
Wednesday night between 10-15 knots.
.PRELIMINARY POINT TEMPS/POPS...
SJU 90 76 87 76 / 40 40 40 30
STT 85 76 84 76 / 50 60 60 30
PR...High Rip Current Risk until 6 PM AST this evening for Culebra-