National Weather Service San Juan PR
534 AM AST Sat Jun 25 2022
.SYNOPSIS...
A TUTT and associated low will linger across the region today
along with a slight increase in low level moisture supporting
afternoon convection. Afternoon showers and isolated thunderstorms
should be focused over areas of the central interior and
northwest sections of Puerto Rico, including around parts of the
San Juan metropolitan area. Expect a light to moderate
southeasterly wind flow across the forecast area today, bringing
warmer temperatures along the north coastal areas of Puerto Rico.
Heat indices between 100 and 110 degrees are expected along
northern portions of Puerto Rico today.
The National Hurricane Center is monitoring a disturbance over
the Atlantic that has a medium chance for formation over the next
5 days. This system is expected to pass by the area to the south
around midweek next week, with no direct impacts to the islands.
However, there is potential for indirect impacts, both on marine
conditions and moisture over the area (and therefore shower
potential). Please monitor future forecasts for updates, including
future forecast discussions (AFDSJU) and Tropical Weather
Outlooks from the National Hurricane Center (TWOAT). But, again,
no direct impacts are expected.
&&
.SHORT TERM...Today through Monday...
Mid to upper level trough (TUTT) and associated low will linger
across the region today, then gradually fill/weaken and lift
northwards Sunday through Monday. Strong surface high pressure
anchored across the north central Atlantic and extending across the
region and a broad surface trough across the eastern Caribbean will
maintain a light to moderate southeasterly wind flow across the
forecast area today, then become more easterly and slightly increase
on Sunday through Monday as the high pressure ridge will build north
of the region. By then, a weak easterly perturbation is forecast to
cross the area bringing a quick surge of low level moisture followed
by a low concentration of suspended Saharan dust particulates.
Recent satellite imagery and doppler weather radar as well as
satellite derived precipitable water products, all suggest frequent
patches of low level moisture crossing the region with embedded
showers. Some showers were being enhanced by the upper trough as
they crossed parts of the islands. So far however the shower
activity has been fast moving and with little accumulations. For
the rest of today a slight increase in low level moisture is
expected. This will support afternoon convection over portions of
the islands. The afternoon showers and isolated thunderstorms should
be focused over parts of the central interior and northwest sections
of Puerto Rico, including around parts of the San Juan metro.
Elsewhere mostly fair weather skies and isolated showers expected.
Some of the enhanced afternoon shower activity may lead to minor
urban and small stream flooding as well as ponding of water on roads
and poor drainage areas but in isolated spots. The prevailing
southeasterly winds will also bring warmer temperatures especially
along the north coastal areas of Puerto Rico. Increasing humidity
may also bring maximum heat indices to between 100 and 110 degrees
along the north portions of Puerto Rico today.
By Sunday, the upper trough is to fill and lift northwards thus
increasing stability aloft. In the meantime the surface high
pressure ridge is to reestablish north of the region resulting in a
more easterly winds and thus favor better transport of trade wind
moisture and the passage of a weak easterly perturbation Sunday
through early Monday. That said, typical passing showers are again
expected during the early morning hours each day followed by lesser
afternoon convection which should be focused mainly over parts of
the central interior and west sections of Puerto Rico. Fewer
streamer-like showers of short duration will be possible around the
San Juan metro and downwind of the U.S. Virgin Islands where mostly
isolated and fair weather skies are so far expected. A low
concentration of Saharan dust particulates is also expected during
that time, as a drier and stable airmass will spread across the
region.
.LONG TERM...Tuesday through Saturday...
With a surface high pressure over the central Atlantic, winds
should be generally easterly to start the forecast period. Tuesday
appears to be the driest day in the long term period as a pocket
of relatively drier airmass in terms of precipitable water values
enters the forecast area. Even so we can still expect some shower
activity in the morning hours mainly over the east and during the
afternoon hours mainly over the western sectors of Puerto Rico.
We are currently monitoring the potential development of a
tropical wave located over the the central tropical Atlantic.
Latest models continue to show the system passing south of the
local area. This system has a 60% chance to develop into a
tropical cyclone within the next five days. As the system moves
south of our region between Wednesday and Thursday, marine
conditions should start to deteriorate and rain bands associated
with this systems could reach the islands. We will continue to
monitor this tropical wave as it continues to move westward and
how potential effects develop as time progresses. A wetter weather
pattern is also expected to persist for the rest of the long term
period, with a lull on Friday as a relatively drier air mass in
terms of precipitable water enters the region. At the end of the
long term period another surge in moisture is currently showed by
the models as an airmass of precipitable water values of around 2
inches engulfs the forecast area on Saturday increasing rain
chances for the region.
&&
.AVIATION...VFR conds across all terminals. SCT SHRA ovr regional
waters and en route btw islands. Few SHRA ovr E interior of PR may
cause brief MVFR and Mtn top obscr due to SHRA/Low brief SHRA cld
lyrs til 25/13Z. SCT OCNL BKN lyrs nr FL025...FL050. SHRA/TSRA will
develop mainly across the interior and west sections of PR btwn
25/16-23z. This activity may affect TJSJ/TJMZ/TJBQ. LGT/VRB Wnds
will bcm fm E-SE around 15 kt with higher gusts and sea breeze
variations after 25/14Z.
&&
.MARINE...
Light to moderate east to southeast winds are expected to
continue. Seas of 6 feet or less are expected in the Atlantic
waters of Puerto Rico and the USVI and the coastal waters north of
Puerto Rico. Small craft operators should exercise caution in
these areas. Seas of 5 feet or less are expected across the rest
of the local waters.
A high risk of rip currents is currently in effect for the north-
central and northwestern beaches of Puerto Rico. The high risk of
rip currents should extend to all northern and eastern beaches by
tomorrow morning and should also extend to the beaches of St.
Croix tomorrow in the evening. These should all end by tomorrow
night.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 90 81 91 81 / 40 40 30 30
STT 83 82 83 81 / 40 40 30 30