National Weather Service Today's Weather Impact Levels

358
FXCA62 TJSJ 240829
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Wed Apr 24 2024

.SYNOPSIS...

The influence of a surface trough will continue to impact the
local weather conditions. Another active afternoon is anticipated
due to the combination of the surface trough, diurnal heating,and
local effects. Winds are forecast to be light today, promoting
slow-moving showers and thunderstorms. With the expected weather,
the potential for urban and stream flooding remains elevated
today.

&&

.SHORT TERM...Today through Friday...

Throughout the overnight hours, satellite and radar detected a band
of showers and cloud coverage stretching from the Caribbean waters
to the Atlantic waters, primarily between eastern Puerto Rico and
the USVI. These showers moved slowly, with the land breeze in
eastern Puerto Rico keeping them mostly over the waters. However,
some moderate to strong showers brushed coastal areas at times.
Eastern coastal portions of Puerto Rico received up to 1.5 inches of
rainfall, with the highest amounts observed in Fajardo and Ceiba. A
similar pattern is expected to continue during the morning hours,
with localized areas across windward coastal sections experiencing
showers that could lead to ponding of water on roads and in poor
drainage areas. In areas with little to no rain, hazy skies will
prevail as suspended Saharan dust particulates continue to move in.
The heat risk for today will be limited across western and northern
coastal areas of Puerto Rico.

The axis of the surface trough remains nearby, with light east-
southeast winds persisting, influenced by an approaching frontal
boundary from the northwest. These winds continue to advect warmer
temperatures across the region. Therefore, another active afternoon
is anticipated due to the combination of the surface trough,
enhanced diurnal heating, marginal instability aloft, and local
effects. Gusty wind conditions may be observed, particularly in the
vicinity of collapsing thunderstorms. However, winds will be mostly
light, which could promote slow-moving showers and thunderstorms.
This will increase the risk of flooding as rainfall accumulations
are enhanced by this factor. Activity will be confined mostly over
interior Puerto Rico, gradually moving west and north as the
afternoon progresses. Heavy showers can also be observed across the
San Juan metro area and downwind of the smaller islands.

By Thursday and Friday, the surface perturbation is expected to have
moved away from the area. However, a mid-level short-wave trough,
along with the aforementioned frontal boundary, will cross the
northeastern Caribbean through the end of the week, maintaining or
even enhancing unstable conditions across the region. Moisture
levels will also remain above normal throughout this period.
According to the GFS Enhanced Galvez-Davison Index, divergence aloft
will peak between Thursday evening and early Friday, with maximum
values expected over the Atlantic waters between Hispaniola and
Puerto Rico. The uncertainty lies in the location of the highest
divergence aloft and whether it coincides with surface heating
during peak daytime hours or remains mostly over the local waters.

Nevertheless, expect wet and unstable weather conditions for the
remainder of the short-term forecast, characterized by alternating
periods of heavy showers and isolated to scattered thunderstorms.
Consequently, the risk of flooding will remain elevated, with the
potential for urban and small stream flooding, along with localized
flash flooding and landslides. Gusty wind conditions and frequent
lightning cannot be ruled out, particularly with the strongest
activity.

.LONG TERM...Saturday through Wednesday....

Lingering moisture from a surface trough will continue to produce a
pattern of passing showers on Saturday, especially during the
morning hours. By later in the afternoon, this moisture will
gradually be pushed south of the local region, as a surface high
pressure exits the eastern coast of the United States. This surface
high will push drier air into the local area and will promote mainly
fair weather conditions for most of the long-term period. The drier
airmass will lower the precipitable water values to around 1.20
inches from Saturday through Tuesday. Moderate to fresh northeast
winds between 15 to 20 mph with higher gusts are expected in
response to the surface high as well. Despite of the drier air
filtering into the local area, there is the chance for shower
development over the local waters at times. These showers may reach
the U.S. Virgin Islands and portions of Puerto Rico. In addition,
afternoon convection is possible across the southwestern portions
of Puerto Rico each afternoon due to the combination of daytime
heating and local effects. Wednesday will be a transition day from
a dry into a much wetter pattern. A field of moisture is expected
to reach the local area from South America increasing the
potential for heavy showers and thunderstorms across the region.
Daytime temperatures are expected to remain in the mid 80s along
the coastal and urban areas of Puerto Rico and the U.S. Virgin
Islands, and in the low 80s across the higher elevations. Heat
indices will stay in the mid to upper 90s.

&&

.AVIATION...
(06Z TAFs)

Expc mainly VFR conditions across all terminals through the forecast
period. However, areas of SHRA and SCT TSRA this aftn could produce
tempo MVFR/IFRcondsandmtnobsc, particularly ovr TJBQ aft 24/17z.
VCTS/SHRA at TJSJ/TJPS for the most part. ESE winds reaching speeds
of up to 8-13 knots, accompanied by higher gusts and sea breeze
variations aft 24/13z. HZdue to Saharan dust, butVSBYshould not
drop more than 7 miles.


&&

.MARINE...

A small northwesterly swell is expected to arrive later tonight into
Thursday. Showers and thunderstorms will continue to affect the
local waters for the next few days. Another surface trough will
strengthen the easterly winds today and Thursday, before becoming
northeast on Saturday under the influence of a surface high pressure
moving off the eastern coast of the United States.


&&

.BEACH FORECAST...

Breaking waves of around 3 feet will maintain the risk of rip
currents generally low today. However, will become moderate again
tonight for the northern beaches of the local islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...CVB
LONG TERM....GRS
AVIATION...CVB

NWS SJU Office Area Forecast Discussion