007
FXCA62 TJSJ 052029
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
429 PM AST Sun May 5 2024

.SYNOPSIS...

The Flood Watch has ended for all of Puerto Rico and the U.S.
Virgin Islands however conditions remain unstable. Persistent
rain could lead to urban andsmall- streamflooding, localized
flashflooding, and debris flow. The local atmosphere`s moisture
content is forecast to remain above normal levels through at least
Thursday, with a drying trend anticipated by the end of the week.
A northerly swell is expected to begin to arrive late Tuesday,
lasting through the end of the week.

&&

.SHORT TERM...Tonight Through Tuesday...

It was a calm morning with light to no wind for many sections of
Puerto Rico and the USVI. However as the sun came out, heat indices
rose to values well over 100 with 113 recorded in Cotton Valley, St.
Croix and nearly as high across other sections across western Puerto
Rico. The first shower was seen over Rio Grande and shortly after
around 2PM thunderstorms started to form across the interior to
northern sections of PR leaving up to around 2 inches in Morovis
and an inch in multiple sections of northern PR. Activity is
expected to linger through the evening hours with more of a
concentration on the interior to northern sections of Puerto
Rico.

A moist local atmosphere with precipitable water values above 2
inches, at least 1 standard deviation above climatological normal,
will exist through midweek. Along with plenty of moisture, an
upper- level jet will persist across the northern Caribbean Basin
through this time, providing ventilation aloft. High pressure
building across the western Atlantic through Wednesday will
maintain a moderate easterly flow across the region, however due
to it`s weaker strength, land breezes are expected to develop
during the overnight hours.

Under these conditions, persistent showers and thunderstorms are
possible at times, especially during the afternoon hours once
diurnal heating, orographic effects, and seabreeze convergence
enhances vertical lifting. For tonight, eastern sections of
Puerto Rico have the best chance to receive rainfall. During the
afternoons of both tomorrow and Wednesday, rain is possible across
most of the area within mainland Puerto Rico. With the strongest
activity there may be flooding impacts due to the much above
normal river streamflows, and saturated soils where any period of
moderate to locally heavy rain could result in dangerous flooding
problems as well as sudden mudslides/landslides. Currently, the
most active day, based on the latest model guidance could be
expected between late Monday into Tuesday with slightly cooler 500
MB temperatures which can increase the chance of thunderstorms.

&&

.LONG TERM...Tuesday through Saturday...
/from previous discussion/

By Wednesday, the latest models agree that a surface high
pressure will remain dominating over the central Atlantic
promoting light to moderate northeasterly to easterly winds
through the end of the workweek. At upper levels, another trough
should move through Thursday, maintaining unstable
conditionsacross the islands with a moist airmass lingering over
the local area. The Precipitable Water (PWAT) models are
suggesting above-normal climatological levelsthrough at least
next Thursday; with values around 1.90-2.20 inches. Consequently,
the wet pattern is expected to continue by midweek with showers
and possible isolated thunderstorms development each afternoon. We
encourage residents and visitors to remain weather-aware because
any additional shower activity over saturated soils will further
enhance the potential for flash flooding and mudslides.

Thursday night into the weekend, a mid to upper-level ridge
extends into the local area from the western Caribbean, bringing a
drier airmass into the upper levels with PWAT values around normal
levels, decreasing the potential for shower development. By Saturday,
the high pressure over the north-central Atlantic will promote
southeasterly winds across our area. As a result, diurnal and
local effects can promote afternoon showers and thunderstorm
activity mainly acrossthe interiorto westernPuerto Rico, but
not expecting significant accumulations since moisture levels
should be lower. In addition, a Saharan Air Layer should be near
the area, but the greater concentrations should stay over the
Caribbean waters.

In summary, expect unstable weather conditions to continue by the
middle of the week, then more stable conditions are anticipated
from Friday onwards.

&&

.AVIATION...
(18Z TAFS)

Mostly VFR conditions expected for the USVI and TJPS terminals this
afternoon, but SHRA and TSRA expected to linger through 22Z around
the Cordillera Central and near TJSJ and TJBQ. Periods of reduced
VIS and low ceilings are expected through this time. SHRA are
expected to increase after 22Z across the Atlantic waters, reaching
the USVI and TJSJ terminals at times, with limited impacts to
operations anticipated. Winds will be light, shifting from the east
around 03-06Z, and then from the NE at 5-8 kts.


&&

.MARINE...

A surface high pressure extending from the western to central
Atlantic will promote light to moderate easterly winds through the
forecast period. A northeasterly swell is expected to spread across
the local waters by Tuesday and gradually increase seas to around 5
to 6 feet through the end of the week. Remnant moisture from the
induced surface trough located to our east will continue to promote
shower and isolated thunderstorms development across the regional
waters during the afternoon and evening for the next several days.


&&

.HYDROLOGY...

The Flood Watch was canceled due to a reduction in expected
rainfall. However sensitive areas should take caution due to the
much above normal river streamflows, and saturated soils where any
period of moderate to locally heavy rain could result in
dangerous flooding problems as well as sudden mudslides/landslides.

&&

BEACH FORECAST...

Low risk of rip currents should continue through Tuesday, then
becoming moderate from Wednesday onwards. However, life-
threatening rip currents often occur in the vicinity of jetties,
and piers.


&&

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

$$

ICP/RVT/RC