Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 260930

Area Forecast Discussion
National Weather Service San Juan PR
530 AM AST Wed Jul 26 2017

SYNOPSIS...TUTT low northeast of the area will prevail through
the end of the workweek. As this feature weakens Friday and into
the upcoming weekend, a weak mid level ridge will build in and
hold through much of the next week. A broad surface high pressure
Will continue to hold through the forecast period. A tropical
wave will continue to move across the area today, increasing the
chance for showers and thunderstorms.


.SHORT TERM...Wednesday through Friday...

A tropical wave brought showers across the local waters, the
northern U.S. Virgin Islands and East Puerto Rico. Little or no
shower activity was detected over the interior sections of Puerto
Rico and St Croix overnight. As tropical moisture pools over the
islands, shower activity is expected to continue across these
areas through the morning hours. Some moderate to heavy rainfall
is possible with this activity and commuters can expect ponding
of water on roads and in low lying areas.

Showers and thunderstorms are expected along and to the northwest of
the Cordillera Central during the afternoon hours. Periods of
moderate to heavy rainfall are expected across these areas. Also,
model guidance continues to indicate favorable conditions for
strong thunderstorms. In addition, winds are expected to shift
from the east-southeast increasing the potential for showers and
thunderstorms in the form of streamers into the San Juan Metro
Area. Across the U.S. Virgin Islands, showers are expected to
form mainly downwind from the islands. Shower activity, on the
other hand, is expected to be limited across the south coast of
Puerto Rico.

As the tropical wave exits the area, a dry air mass is expected
to reach the islands resulting in mostly clear skies but with
Saharan dust particles, as the model guidance is indicating.
Another tropical wave is forecast to reach the islands on Friday.
At this time, moisture seem to be less abundant on Friday, but
showers and thunderstorms are still expected to form across most
of the islands.

.LONG TERM...Saturday through Thursday...

A weak mid level ridge is expected to hold across the area through
the forecast period. At lower levels, a broad high pressure across
the central Atlantic will continue to prevail, resulting in east to
east southeast winds through Tuesday. Precipitable water is expected
to remain near the normal range which is 1.75 inches Saturday through
early next workweek. Moisture advection is expected by midweek as an
easterly disturbance moves across the area. Therefore, under the
lack of upper level forcing and moisture content near the normal
range; continue to expect a seasonable weather pattern with trade
wind showers across the USVI and E PR at times, as well as showers
and thunderstorms developing across west sections of Puerto Rico
in the afternoon. The highest chance for widespread shower activity
with thunderstorms looks possible at the end of the forecast


.AVIATION...SHRA are expected to continue across the Flying area
as a tropical wave moves through the region. SHRA/TSRA are
expected to develop across the interior and NW quadrant of PR as
well as downwind from El Yunque. As a result, VFR or even IFR
conditions are possible aft 26/15z across TJBQ/TJSJ. SHRA/TSRA are
possible in the VCTY of TIST/TISX/TJPS. Wx conds will improve aft
26/23z. Calm to light/VRB winds increasing at 10 to 15 kt with
higher gusts in and near SHRA/TSRA aft 26/14z.


.MARINE...Tranquil marine conditions will continue to prevail
across the forecast area with seas 3 to 5 feet and occasional
seas up to 6 feet. Winds 10 to 15 knots to continue. Passing
tropical wave will continue to bring periods of showers and
isolated thunderstorms across the local waters.


SJU  90  80  90  80 /  50  30  30  20
STT  89  80  90  80 /  50  60  30  30




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