Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 240912
Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Fri Mar 24 2017
.SYNOPSIS...Deep layered moisture and trof pattern aloft will
maintain an unsettled weather pattern through the weekend. At low
levels, a surface trough and developing low north of Hispaniola
will continue to create a moist 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
.SHORT TERM...Friday through Sunday...
Mostly cloudy skies prevailed across the local islands overnight and
early this morning with shower activity observed across the Caribbean
waters, the eastern half of Puerto Rico as well as the U.S. Virgin
Islands. Rainfall accumulations across the USVI were between one and
two inches with minimal accumulations noted over Puerto Rico.
Temperatures along coastal areas were in the mid to upper 70s under
light and variable winds.
The local weather regime will continue to be dictated by a mid to
upper level trough which is located across the western Atlantic and
into the central Caribbean. The trough aloft and associated upper
level divergent pattern will persist through early next week.
Although the jet maxima remains north of the forecast area during
the entire period; is close enough to destabilize the local atmosphere.
At lower levels, an induced trough across the northeast Caribbean,
which is associated with the aforementioned trough, is expected to
develop into a low by Sun. This will continue to support moisture
advection from the southeast during the next few days.
Therefore, under plenty of moisture and favorable upper level
dynamics, environmental conditions are favorable and conductive for
shower and thunder activity across the area. Based on the latest
guidance, the best chance for periods of showers and Tstorms is
expected across east and southeast Puerto Rico as well as the U.S.
Virgin Islands Fri and Sat with a slightly decrease in coverage and
intensity on Sun. Shower and thunder activity across northwest Puerto
Rico will be locally induced and enhanced by the proximity of the
trough aloft. These showers likely to result in urban flooding as well
as rises along small streams and rivers particularly across eastern
.LONG TERM...Monday through Friday.
Surface low is forecast to move north of the islands through early
next week across the Central Atlantic. Creating a south to
southwesterly wind flow through at least late Tuesday night. As
the low pulls away, moisture content is expected to diminish
quickly as a strong surface high pressure develops over the
Western Atlantic and moves slowly north of the islands through the
forecast period. At the moment, best chance for showers are
expected between eastern/northern PR and the USVI on
Monday/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 fair
weather conditions across the islands.
.AVIATION...MVFR or even IFR conds at times will remain possible through
the forecast period at all PR and USVI TAF sites, particularly
JSJ/IST/ISX. Mountain obscurations expected throughout the day. Mostly
VFR conds at the Leeward terminals. East southeast winds at 10 knots or
.MARINE...Coastal buoys are indicating seas around 4 feet and
variable winds at less than 10 knots. A northerly swell is
forecast to reach the local Atlantic waters late tonight and
increase through the weekend across the rest of the northern
waters of the islands and passages. Small craft advisories will be
in effect. A high risk of rip currents is expected across much of
the north facing beaches of the islands during the weekend.
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 72 85 73 / 70 50 60 50
STT 82 73 81 74 / 70 60 70 50
AM...Small Craft Advisory from 2 PM Saturday to 2 PM AST Sunday
for Anegada Passage Southward to 17N.
Small Craft Advisory from 8 AM Saturday to 2 PM AST Sunday for
Coastal Waters of Northern Puerto Rico out 10 NM-Mona
Passage Southward to 17N.
Small Craft Advisory from 2 PM Saturday to 8 AM AST Sunday for
Coastal Waters of Northern USVI and Culebra out 10 NM.
Small Craft Advisory from 8 AM Saturday to 8 AM AST Sunday for
Coastal Waters OF Northwestern Puerto Rico out 10 NM.
Small Craft Advisory from 2 AM Saturday to 8 PM AST Sunday for
Atlantic Waters of Puerto Rico and USVI from 10 NM to 19.5N.