National Weather Service San Juan PR
525 AM AST Mon Aug 31 2020
.SYNOPSIS...
Moisture associated with a tropical wave, monitored by the
National Hurricane Center and moving off to the south of the
islands, across the eastern Caribbean Sea, will exit the region
today. Another tropical perturbation will reach the northeast
Caribbean later today, increasing shower activity and winds
locally. The axis of this perturbation will cross the islands of
Puerto Rico and the U.S. Virgin Islands on Tuesday. The chance for
shower/thunderstorm development will continue throughout the
work-week, with high uncertainty on the behavior of several
tropical waves across the Tropical Atlantic.
&&
.SHORT TERM...Today through Wednesday...
The moisture associated with a strong tropical wave, monitored by
the National Hurricane Center, located well at our south over the
eastern Caribbean Sea, will continue to move out of the forecast
area today. Therefore, showers will continue to move across the
northern half portion of Puerto Rico, the U.S. Virgin Islands and
surrounding waters this morning. Then, moisture is expected to
increase as the leading edge of another tropical perturbation
move across the islands from the northeast.
Total Precipitable Water (TPW) associated with the aforementioned
tropical disturbance will increase between 1.8 and 2.5 inches late
this afternoon into the evening hours. This feature will bring
scattered to widespread shower and thunderstorm activity over
Puerto Rico and the US. Virgin Islands. The axis of the wave will
move across the islands on Tuesday. As a result, favorable weather
conditions for the development of showers and thunderstorms will
continue through the short term forecast. Urban and small stream
flooding will remain possible each afternoon with the strongest
activity.
Showers associated with the lingering tropical moisture will
continue to affect the islands on Wednesday. Easterly winds,
diurnal heating and local effects will aid in afternoon
convection over the western and interior sections of Puerto Rico.
A more drier air mass with Saharan dust is forecast to filter
into the region by the end of the short-term period. Maximum
temperature are expected between the upper 80s and low 90s across
the coastal and urban areas in Puerto Rico and the U.S. Virgin
Islands each day.
.LONG TERM...Thursday through Monday...
An upper-level trough will amplify over the Northeast-Caribbean
ramping-up local instability. This feature aloft will induce a set
of surface troughs lifting surface tropical moisture from the
southern Caribbean into Puerto Rico and the U.S. Virgin Islands.
There is a good agreement between meteorological guidance about
these features, as well as an increase in the available tropical
moisture, therefore, expect showery weather with afternoon
convection each day. As the trough moves westward over the
Hispaniola, ventilation aloft will promote better convection
across the region late Thursday night into Friday. The
aforementioned upper-level feature will move over the Windward
Passage, between Haiti/Cuba, by next weekend.
There is plenty of uncertainty about the possible weather
conditions across the tropical Atlantic for the weekend and early
next week. That said, islanders cannot rule out the typical
passing showers across the windward sections each night/morning,
followed by afternoon convection across the western sections. We
encourage people with interest in the Northeast Caribbean,
including PR and the USVI, to watch the weather evolution in the
Tropical Atlantic by following the products from the National
Hurricane Center and your Weather Forecast Office in San Juan.
&&
.AVIATION...
VFR conditions are expected to prevail through 31/15Z. Some
haziness associated with the remnants of a Saharan air mass is
expected today. However, VIS is expected to remain P6SM. Easterly
winds will persist today, and will increase at 10 to 20 knots
after 31/13z. SHRA/TSRA will develop along and to the west of the
Cordillera Central between 31/15-22z. Also, this wave will bring
SHRA/TSRA across the islands and could impact ISX/IST/JSJ.
&&
.MARINE...
Mariners can expect choppy seas during the next few days, with
wave-heights up to 6 feet. A tropical wave will exit the region to
our south today, and a second perturbation will move into the
northeast Caribbean, increasing showers and winds today and
tomorrow. Therefore, small craft operators should exercise caution
due to easterly winds between 15 and 20 knots across most of the
local waters.
There is plenty of uncertainty with a set of tropical waves, one
near the Cabo Verde Islands and another forecast to move away from
the African coast. Therefore, keep vigilant of the weather
conditions across the Tropical Atlantic by following the products
from the National Hurricane Center and your Weather Forecast
Office in San Juan.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 80 89 78 90 / 60 80 50 40
STT 82 88 79 90 / 70 70 40 40