National Weather Service San Juan PR
446 AM AST Mon Dec 28 2020
.SYNOPSIS...
A surface induce trough is expected to mover the region increasing
the potential for shower activity over the region today,.
Therefore, minor flooding and ponding of water in roadways are
expected. For today, choppy marine conditions with seas up to 6
feet over the Atlantic showers. There is a high risk of rip
current for the north-facing beaches of Puerto Rico.
&&
.SHORT TERM...Today through Wednesday...
A SFC shortwave trough will be approaching the local islands later
today, causing an increase in instability and moisture to the local
islands. Therefore, an increase in cloudiness and shower activity is
also expected. For that reason, widely scattered showers are
forecast across the local area, while locally numerous showers are
forecast this afternoon across the interior and western sections of
Puerto Rico. However, confidence is moderate because of significant
discrepancy in the model guidance. The high resolution models are
much more bullish that then global GFS and ECMWF models, which show
very little rain.
By Tuesday, a SFC high pressure will move into the western Atlantic,
which will push a frontal boundary to the north of the local area.
That said, the model guidance has backed off a little on the
rainfall activity expected on Tuesday, keeping near normal moisture
but advecting drier air from the north, which would limit
significant shower activity but isolated to scattered brief showers
continue to be expected. However, cloudiness and shower activity is
expected to increase significantly on Wednesday afternoon, with
perhaps even a few thunderstorms as the frontal boundary moves over
the local area.
.LONG TERM...Thursday through Monday...
A strong surface high pressure over the central Atlantic will
result in a more east-northeast wind flow over the region between
Thursday to Friday. As the aforementioned feature moves into the
western Atlantic, a drier air mass is expected to filter into the
region with the precipitable water content between 0.8 to 1.2
inches. According to model guidances, Saturday is the best day for
shower activity as a back door frontal moves over the region. An
increase in low-level moisture is expected, therefore, shower
activity could develop over the local islands. However,
significant rainfall accumulations are not expected due to the
fast-moving shower.
On Monday, a surface high pressure over the western Atlantic will
create a move east-southeast wind flow over the region. Therefore,
low-level moisture embedded in the winds will increase cloudiness
and shower activity over the local islands.
&&
.AVIATION...
VFR conditions are expected across the local terminals thru at least
28/16Z. VCSH expected across the local terminals today with possible
TEMPO SHRA, but kept out of TAF due to timing uncertainty. Winds
generally at around 5 to 10 kts today from the east at ISX and IST,
but with a northerly component at TJSJ and TJBQ, southerly at
TJPS.
&&
.MARINE...
Choppy marine conditions are expected for today across the
Atlantic offshore waters with seas up to 6 feet. Elsewhere, seas
between 3 to feet are expected. Hazardous marine conditions are
expected once again for mid week as winds gradually increase over
the local waters. As a induce surface trough move over the area,
isolated to scattered showers are forecasted over the area.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 83 74 / 30 30 50 40
STT 83 72 83 74 / 30 50 50 40