National Weather Service San Juan PR
453 AM AST Sat Jun 26 2021
.SYNOPSIS...A tropical wave will increase shower and thunderstorm
activity across the local area today. Moisture associated to the
wave lingers through Sunday. A Saharan Air Layer is expected to
cause hazy skies early in the workweek. Another tropical wave is
forecast to move across the area by midweek.
&&
.SHORT TERM...Today through Monday...
A tropical wave is expected to move across the area today and bring
a gradual increase in moisture as well as switch the low-level winds
from the southeast. A Tropical Upper Tropospheric Trough (TUTT) will
be located north of the area and will provide some upper-level
divergence. Even though the best forcing and best moisture
associated with these features will remain north of the islands, the
modest increase in moisture and forcing for ascent will be
sufficient to aid in the increase in shower and isolated
thunderstorm activity for today. Passing showers are expected across
portions of the USVI and eastern Puerto Rico through the morning
hours followed by activity developing across the northwestern
quadrant of Puerto Rico during the afternoon hours as the moisture
and forcing aloft will combine with daytime heating and local
effects to result in moderate to heavy showers and isolated
thunderstorms. Urban and small stream flooding will be possible with
the heaviest and most persistent activity. There are some
indications amongst some high resolution and global model guidance
for better low-level moisture and divergence aloft over the area for
tonight and as a result an area of more organized convective
activity may develop, resulting in more numerous showers as well as
isolated thunderstorms, mainly across eastern and southeastern
portions of Puerto Rico.
The tropical wave will move west of the area on Sunday.
Nevertheless, lingering moisture will still be in place to result in
isolated to scattered showers across portions of eastern Puerto Rico
and the USVI during the morning hours followed by afternoon
convection across northwestern Puerto Rico.
By Sunday night through Monday, a drier and more stable pattern will
be settling over the area as the western periphery of a mid-level
ridge over the central Atlantic will move over the northeast
Caribbean. Therefore, a mainly fair weather pattern is expected.
Nevertheless, some limited afternoon convection may still develop
over northwest Puerto Rico Monday afternoon.
.LONG TERM...Tuesday through Saturday...
A Saharan Air Layer is expected to move on Tuesday and continue
through at least midday Wednesday, this will cause hazy skies and
limit shower activity across the islands. However, diurnally
induced afternoon showers are still expected to develop on Tuesday
over western Puerto Rico. Increasing trade winds are also
expected, and brief passing showers could move at times across the
U.S. Virgin Islands and eastern sections of PR, however, no
significant rainfall accumulations are expected at this time.
Meanwhile, latest model guidance continues to suggest that a
tropical wave will move between Wednesday night into Thursday
across the local area. Shower and thunderstorm activity is
expected to increase during this period across the regional waters
and across PR and the USVI. This wave currently has a low
formation chance to develop during the next 5 days into a tropical
cyclone according to the National Hurricane Center.
A strong ridge is forecast to build across the Atlantic basin
during the latter part of the week, and another area of the SAL
with drier air is expected to move over the islands and promote
fair weather conditions into the weekend. Another tropical wave is
forecast to move on Friday, well south of the region.
&&
.AVIATION...Mostly VFR conditions expected across area terminals
throughout the period. However, VCSH are expected across eastern PR,
the USVI, and Leeward Island terminals throughout the period due to
a tropical wave passing over the area. VCTS expected across TJBQ
between 26/16z and 26/22z. Brief MVFR conditions are possible,
especially if SHRA activity moves over the terminals. Winds are
expected to be light and variable through 26/12z, increasing to 10
and 15 knots from ESE-SE with sea breeze variations after 26/14z.
&&
.MARINE...A tropical wave will increase shower and thunderstorm
development across the local waters through Sunday. Seas should
range between 3-5 feet through the weekend. Moderate east to
southeast trades will prevail, however, strong gusty winds are
expected with the thunderstorms. There is a moderate risk of rip
currents for the northern beaches of Puerto Rico and the eastern
beaches of St. Croix.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 87 77 / 50 50 50 30
STT 87 77 87 78 / 50 50 50 30