National Weather Service San Juan PR
423 AM AST Sun Jun 4 2023
.SYNOPSIS...Above normal moisture will continue to be steered
into the island by breezy southern winds. Due to the combination
of high temperatures and moisture, high heat indices are expected
once again from late morning to the afternoon hours. A drier
pattern is expected to start late tomorrow into Tuesday as winds
become more southeasterly and more Saharan Dust filters in.
&&
.SHORT TERM...Today through Tuesday...
The Doppler radar summary since midnight indicates slight rainfall
accumulation across the southern half of Puerto Rico, and also for
Vieques and Culebra. No rain was detected over the Virgin Islands.
This rain was the result of passing showers reaching the coastal
areas from the Caribbean Sea.
No significant changes were introduced to the near term forecast,
except to reduce the probability of precipitation late Monday and on
Tuesday. The general pattern is still dominated by a deep layer high
pressure over the eastern Atlantic and a deep layer trough centered
near Cuba. These features are driving the low and mid level winds
from the south today and tomorrow. Under this pattern, temperatures
will continue to warm up, reaching the mid 90s along the coastal and
urban areas of Puerto Rico, and the upper 80s to low 90s along the
Virgin Islands. The wind flow will also maintain the moisture levels
above normal, with precipitable water values around 2.0 inches. With
the combination of hot temperatures and high humidities, heat
indices are again expected to surpass 111 degrees along north-
central Puerto Rico...above 108 for Culebra, the northeast,
northwest, around Mayaguez, and in the urban and valleys of the
eastern interior...and from 102 to 107 for the southern coast of PR,
Vieques, and all of the U.S. Virgin Islands. The heat will not give
way, and above normal temperatures will persist throughout the end
of the forecast period.
On Tuesday, the upper level trough will lift and the high pressure
will make the winds to back a little, becoming out of the southeast.
Winds will remain enhanced too, with the low level wind steering
flow at 20 knots today, and around 15-18 kts on Monday and
Tuesday. Additionally, the aerosol models indicate that Saharan
dust will increase in concentration, resulting in hazy skies, with
higher concentrations on Monday and Tuesday. Finally, discussing
rainfall probabilities, the mid to upper level high will result in
unfavorable conditions for strong showers to develop. However,
passing showers will continue to move across the southern
municipalities of Puerto Rico, resulting in wet roads and ponding
of waters in areas of low elevation.
&&
.LONG TERM...Wednesday through Sunday...
No major changes to the long term forecast. A surface high pressure
northeast of the region will promote more southeasterly winds and
steer a Saharan Air Layer (SAL) over the islands. Model guidance
indicates higher concentrations on Thursday, where Aerosol Optical
depth could reach more than 0.20 over the islands, above the 75th
percentile. Saharan dust will continue to linger for most of the
period, promoting hazy skies. A mid- to upper- level ridge will
dominate the region and mostly dry air will be present above 850 mb.
This will limit convective development and promote stability over
the islands. In terms of Precipitable Water (PWAT) values, these
should remain at normal to below normal for this time of the year
with the driest day being Thursday, with PWAT values around or below
an inch. Model guidance now seems in more agreement with an increase
in moisture for Friday. Frontal moisture remnants that moved around
the surface high pressure will be steered towards the region on
Friday promoting an increase in PWAT values. Patches of both drier
and humid air will reach the region during the weekend but an
overall drying pattern will be observed. The seasonal weather
pattern will vary in intensity depending on moisture content; on
days with more moisture, passing showers across windward sectors of
the islands and afternoon convective activity due to diurnal heating
and local effects will be more likely. High heat indices are
expected each day, reaching 105 degrees to the 110s, especially
across lower elevations of northern and western Puerto Rico.
&&
.AVIATION...Mainly VFR conditions expected to prevail. Passing
SHRA expected to move at TJPS through the period, with brief
periods of reduced VIS and low ceilings possible. HZ due to
Saharan dust is expected, but with VIS remaining at P6SM. Winds
will be from the south at 13-20 kts, and stronger gusts.&&
&&
.MARINE...Moderate to locally fresh south to southeasterly winds
will continue across the region. Small Craft Should Exercise
Caution mainly over the offshore Atlantic, eastern waters, western
waters and the Mona Passage due to these winds. Expect seas 4
feet or less over the local waters. There is a low risk of rip
currents for all of the local beaches.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch until 10 AM AST this morning for PRZ001-005-
008.
Excessive Heat Watch from this afternoon through Tuesday
afternoon for PRZ001-005-008.
Excessive Heat Warning from 10 AM this morning to 5 PM AST this
afternoon for PRZ001-005.
Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ002-004-008-010-012.
VI...None.
AM...None.
&&
$$
SHORT TERM...ERG
LONG TERM....MRR