National Weather Service San Juan PR
421 AM AST Wed Mar 24 2021
.SYNOPSIS...
Showers and possibly even a few weak thunderstorms are possible
later today due to above average moisture and favorable
atmospheric conditions. Calmer weather is expected for later in
the week due to the influence of an upper level ridging. Above
average moisture and scattered showers are in the forecast for
next week. Calmer seas will prevail with the return to wind-driven
hazardous seas for this weekend.
&&
.SHORT TERM...Today through Friday...
A weak trade wind cap will allow low-level moisture to increase
today. An area of precipitable water (PWAT) content of around 1.50
inches is currently moving across the Leeward Islands and will reach
the local area during the day. At upper levels, a ridge is building
west of the region, while the trough is moving further east and away
of the region. An induced low-to-mid level trough will promote an
east to northeast wind flow and an advective pattern, that will
favor night/early morning showers across the U.S. Virgin Islands and
portions of east/northeast Puerto Rico.
For today, due to the proximity of the upper level trough and surge
in low-level moisture, scattered to locally numerous showers with
isolated thunderstorms cannot be ruled out in diurnal convection
over portions of the interior and west/southwest PR. Urban and small
stream flooding is possible with this activity. At least through
Friday, PWAT content is forecast to continue between 1.20-1.40
inches, but at the same time, stability aloft should gradually
increase as the upper level ridge strengthens west and over the area.
.LONG TERM...Saturday through Wednesday...
Long range models continue to suggest an upper-level trough to our
east for the weekend, with a mid to upper level ridge way off to the
west. The trough will bring in cooler air aloft and encourage upward
motion and the formation of more potent showers for Saturday and
possibly Sunday as well. However, a few factors will act to limit
the impact of these showers. Surface high pressure to our north will
keep east-northeasterly winds fairly breezy, thus the showers will
move quickly. Furthermore, there will not be much moisture to work
with, and mid-levels are forecasted to be particularly dry. Thus,
scattered showers will be possible for northeast Puerto Rico for
Saturday and Sunday morning, with afternoon showers and possibly
isolated thunderstorms for western and southwestern Puerto Rico.
These showers will likely move fast enough so that flooding will
not be an issue, but ponding of water over roadways is possible.
For the beginning of the workweek, we lose the forcing from the
upper level trough as it moves off to the east, but moisture
associated with the trough will decouple from the trough and move
westward into our region. Winds are expected to remain easterly
to east-northeasterly and quite brisk. So fast moving showers will
continue to impact eastern and northern Puerto Rico in the
morning hours. With afternoon moderate shower activity for western
and southwestern Puerto Rico. Winds in the long-term forecast
look brisk enough that the marine conditions will be negatively
impacted.
&&
.AVIATION...Mainly VFR conditions are expected to prevail across all
the terminals during the next 24 hours. However, SHRA is expected to
develop in and around TJSJ/TIST/TISX from 15z-21z, causing tempo
MVFR conds. Also, there is a chance for TSRA in and around TJPS fm
16z-22z. East to northeast winds btw 8-15 kt with sea breeze
variations expected after 14z.
&&
.MARINE...
Seas will be fairly tranquil for the next few days, with wave
heights generally below 5 feet, and regional buoys now reflect
these calmer seas. Seas will become choppy once again as winds
pick up on Friday and through the weekend. Small Craft Advisories
will likely be issued for wind-induced swell event. Isolated
showers will continue over the local waters.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 85 74 / 30 40 30 40
STT 84 73 85 73 / 50 30 30 30