Areal Flood Warning 27, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
158 PM AST Sun Nov 13 2016

.SYNOPSIS...easterly trade winds with moisture and troughiness
will continue in the local area with scattered showers. A cold
front is likely to drop into the forecast area next weekend to
increase shower activity and lower temperatures a few degrees.

At upper levels...High pressure will dominate the Caribbean Sea
until Friday night. A moderately strong trough will move off the
Atlantic coast of the United States this Wednesday. A low will
cut-off Thursday night or Friday and drop south causing the sub-
tropical jet to dip within 80-160 miles of Puerto Rico by Sunday.

At mid levels...High pressure over the Caribbean Sea will become
centered over Saint Thomas by Wednesday. A low will form as a
trough leaves the Atlantic coast of the United States near
Washington DC and dip to as close as 31 north Friday through
Sunday. Mid-level moisture is quite limited except for a
boundary-layer passage on Saturday.

At lower levels...A weakening trough/tropical wave near 52 west
will approach the Lesser Antilles early this week causing local
flow to remain mainly easterly. Low pressure just off of the
Florida coast will move quickly north in the western Atlantic.
Moderately strong high pressure will become stalled over the
eastern coast of the Untied States Thursday while that low
pressure returns to the south in the vicinity of 50 west. This and
the mid level low mentioned above will cause a cold front to move
into the forecast area on Saturday with increased moisture and
shower activity.

&&

.DISCUSSION...Moisture continued in easterly flow causing showers
to form from Humacao to Toa Baja. Some areas will receive more
than one inch in a narrow band. Other showers formed along the
Cordillera Central from Mayaguez to Coamo. Up to now thunderstorms
had not been observed.

Easterly flow will continue and prevailing moisture will drive
early morning passing showers as well as more active convection
over higher terrain and areas of local convergence during the
afternoons. A few thunderstorms will also remain possible.
Moisture continues over the area through Monday, decreases
slightly the first half of the work week and then increases
through Saturday with the approach of a cold front. The driest
weather of the next 10 days is promised Monday morning of next
week when precipitable water drops below 1 inch.

This is a likely scenario, but confidence in the models is
medium-low. The GFS has changed from a strong trough deepening
over the western Caribbean to a strong tropical low advancing on
Hispaniola late in the 15 day period to a tropical low moving
into the Pacific (13/06z run) and back to a weak tropical low
that approaches Jamaica. This leads to considerable uncertainty as
to whether the features necessary to bring the cold front this far
south will materialize. That said, although these are considerable
changes for the western Caribbean, they have not been
particularly significant for the local area as moisture and modest
instability will continue to bring scattered showers and warm
temperatures though much of the week.

&&

.AVIATION...SHRA/TSRA will continue to impact the flying area
of TJSJ/TJPS/TJBQ/TJMZ for the rest of the afternoon hours.
Mtn top obscd and tempo MVFR conds possible through 22z. Streamers
off the USVI will continue to create mainly VCSH with possible -RA at
TIST. Mainly VFR conditions expected after 23z through at least
14/16z. ESE low level winds are expected to become ENE after
14/00z around 9-15 kts. However, light and variable winds are
expected at sfc overnight.

&&

.MARINE...Seas will continue to diminish slowly through Monday,
increase slightly and then decrease until Friday. The approach of
a cold front will increase winds and seas, but small craft
advisories are no longer as certain.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  87  78  87 /  40  40  40  40
STT  77  86  78  86 /  40  40  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

13/12