085
FXCA62 TJSJ 192041
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
441 PM AST Sat Apr 19 2025

.SYNOPSIS...

The combination of a mid-to-upper-level trough and surface-
induced trough, as well as available moisture, will continue to
promote a moist and unstable pattern tonight through Sunday
morning. Therefore, periods of strong showers with thunderstorms
will promote an elevated potential for urban flooding and minor
small- stream flooding. Marine and coastal conditions will also
deteriorate with a Small Craft Advisory starting this evening for
the offshore Atlantic waters, and a High Risk of Rip Currents
starting tomorrow for the north-oriented beaches of Puerto Rico.


&&

.SHORT TERM...Tonight through Monday...

A very active day in terms of rainfall was observed across Puerto
Rico today due to the influence of a mid-to-upper-level trough, in
combination with a surface-induced trough. During the morning, a
thunderstorm developed over the northwestern tip of Puerto Rico,
bringing heavy rain and occasional lightning, leaving behind 1 to
1.5 inches of rainfall. At the same time, passing showers moved
across most of northern and eastern Puerto Rico. From mid-morning
onward, some of these showers, accompanied by isolated
thunderstorms, began to strengthen, resulting in multiple Flood
Advisories across various sectors. Later, the heaviest showers and
thunderstorms shifted over southern Puerto Rico. Based on radar
estimates, general rainfall totals ranged between 2 to 3 inches,
with isolated higher amounts.

For the rest of the afternoon, conditions are expected to gradually
improve after sunset. However, additional showers and thunderstorms
are expected to continue before then, potentially causing ponding of
water on roadways and in poorly drained areas.

Not many changes were made to the forecast, as it remains largely on
track. Weather conditions will continue to be influenced by the mid-
to-upper-level trough, which is expected to linger through tomorrow.
In combination with the surface-induced trough, this pattern will
continue to dominate the regional weather and enhance low-level
convergence across the northeastern Caribbean. According to the
latest model guidance, precipitable water values are forecast to
range from 1.7 to 1.9 inches through tonightabove the
climatological average for this time of year. By tomorrow (Sunday),
these values will begin to decrease to near-normal levels.
Therefore, tomorrow will be more as a transition day. Expect showers
mainly over the surrounding waters and eastern Puerto Rico during
the morning, with a limited flood risk early in the day. Some
afternoon convection may still develop, supported by available
moisture and local effects, but overall conditions will be less
favorable for deep convection. As a result, a gradual improvement in
rainfall conditions is expected later in the day and continuing into
early next week.

.LONG TERM...Tuesday through Saturday...

Current model guidance has precipitable water values (PWAT) at 1 to
1.20 inches to start the long term period, gradually increasing as
we continue into the period. To start the period, a mid to upper
level trough will be northeast of the islands, gradually
deteriorating as we head in to the midweek. A surface trough,
however, will continue to cross the region, promoting east-
northeasterly steering flow on Tuesday, gradually backing to
become southeasterly by Wednesday. An more east-southeast Thursday
and into the weekend. A notable increase in PWAT values is
forecast by late Thursday, with most of the region having more
than 1.5 inches of PWAT, with the eastern region having around 2.0
inches. By late Saturday, current model guidance has most of the
region at around 2.0 inches (above normal values for this time of
the year). Most available moisture will be confined to below 700
mb through at least late Friday. In general, weather conditions
are forecast to gradually improve during the start of the next
workweek, overnight and morning showers are still forecast over
windward areas while afternoon convection will still occur over
sectors of western PR, with exact locations depending on the
prevalent steering flow that day. The increase in moisture to end
the workweek and into the next weekend can increase the coverage
of this activity. 925 mb temperatures are forecast to be at below
to normal values to start the period, gradually climbing due to
east-southeast flow during the second half of the workweek.


&&

.AVIATION...
(18Z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, a sfc trough will continue to
result in SHRA/isold TSRA till 20/06Z across most TAF sites with lcl
MVFR, and brief IFR, and clds topping mtns. NE winds at 12-17 kt
with higher gusts and sea breeze variations till 19/23z  bcmg land
breezes of less than 12 knots aft 19/23Z.


&&

.MARINE...

A surface high pressure system over the western Atlantic will
continue to push remnant showers of a past frontal boundary across
the region over the next few days while a nearby mid to upper level
trough and a surface trough produces favorable conditions for their
development. This will lead to increased showers and thunderstorms
across the local waters. Increasing northeasterly winds and a weak
northerly swell will deteriorate marine conditions by this evening
and into early next week. A Small Craft Advisory is in effect for
the offshore Atlantic Waters and later on for the Anegada Passage
the Atlantic near shore waters.

&&

.BEACH FORECAST..
A low to (in some areas of north-central and northwestern PR)
moderate risk of rip currents is expected today. Tonight, the risk
increases to moderate for all north-oriented beaches of Puerto
Rico. Life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers.

For tomorrow, Sunday, increasing winds and a weak northerly swell
will further deteriorate coastal conditions. A High Risk of Rip
Currents is forecast for the north-oriented beaches of Puerto
Rico, from Rincon to Fajardo, through at least early Tuesday. A
High Risk of Rip Currents means that life-threatening rip
currents are likely in the surf zone.

If you become caught in a rip current, yell for help. Remain
calm, do not exhaust yourself and stay afloat while waiting for
help. If you have to swim out of a rip current, swim parallel to
shore and back toward the beach when possible. Do not attempt to
swim directly against a rip current as you will tire quickly.

Beachgoers should also remain vigilant for afternoon thunderstorms,
especially along the western and southwestern coasts of Puerto
Rico this weekend, where dangerous lightning may occur.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from Sunday morning through late Monday
     night for PRZ001-002-005-008.

     High Rip Current Risk from Sunday morning through late Sunday
     night for PRZ010.

VI...None.
AM...Small Craft Advisory until 6 AM AST Tuesday for AMZ711.

     Small Craft Advisory from noon Sunday to 6 AM AST Monday for
     AMZ712-742.

     Small Craft Advisory from midnight tonight to 6 AM AST Tuesday
     for AMZ741.

&&

$$

SHORT TERM...EM
LONG TERM....GRS
AVIATION...EM