375
FXCA62 TJSJ 171802
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
202 PM AST Thu Sep 17 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 148 PM AST Thu Sep 17 2026

- Showers and thunderstorms have developed again this afternoon,
particularly across interior and northwestern Puerto Rico. Activity
has been less widespread than yesterday but will continue through
the rest of the afternoon.

- Another round of showers and thunderstorms is possible Friday
afternoon, especially across western Puerto Rico.

- Hot conditions will become more noticeable over the next few days.
Heat impacts are expected to remain limited this afternoon, increase
Friday, and become more significant by this weekend.

- A moderate risk of rip currents will continue through Friday along
some beaches of Puerto Rico and the U.S. Virgin Islands.

&&

.Short Term(This evening through Saturday)...
Issued at 148 PM AST Thu Sep 17 2026

Passing showers and isolated thunderstorms have been increasing and
progressing from southern to northwestern Puerto Rico early this
afternoon, as moisture associated with the tropical wave is dragged
in by an ESE flow. Following this pattern, additional shower and
thunderstorm activity is anticipated to develop mainly over eastern,
northern, and northwestern Puerto Rico, driven by the combination of
trailing moisture from the tropical wave and local effects (i.e.,
orographic effects, sea breeze convergence, and daytime heating).
Later tonight, a drier air mass is expected to move across the area.
However, lingering moisture from the tropical wave could still
support convection on Friday, with PWAT values remaining between
1.95 and 2.20 inches. The strongest showers and thunderstorms will
likely occur tomorrow afternoon, although passing showers moving
across eastern Puerto Rico and the USVI during the morning hours
cannot be ruled out, as winds are expected to gradually shift to a
more easterly flow tonight. As the moisture associated with the
tropical wave departs the area, the weather pattern is expected to
become more seasonal, with convection mainly developing over the
interior and extending into western and northwestern Puerto Rico in
the afternoon.

Based on this scenario, an excessive rainfall risk remains elevated
today across portions of eastern, northern, and northwestern Puerto
Rico, while a limited excessive rainfall risk is expected for the
rest of the CWA. These risk levels will persist into Saturday;
however, the elevated risk will become increasingly confined to the
western and northwestern portions. By Saturday, the elevated risk
will be isolated to the western portions, with a limited risk over
the interior, metropolitan, and other remaining areas. These risk
levels mean that flooding is possible in urban areas, roads, and
small streams and washes. Additionally, ponding of water on roads
and in poorly drained areas is possible across most of the region.
Given the rainfall received over the past few days, landslides are
also possible due to high soil saturation over the interior and
eastern portions of Puerto Rico.

The excessive heat risk is expected to gradually increase heading
into Saturday. It will remain limited today due to cloud cover,
become elevated by Friday as cloud cover diminishes, and could reach
significant level by Saturday due to clearer skies and winds
shifting to a more southeasterly flow, which will promote high heat
indices across the CWA. A significant level of heat risk affects
anyone without effective cooling and/or adequate hydration. In
addition, impacts are possible in some health systems, heat-
sensitive industries, and infrastructure. We recommend that
individuals avoid outdoor activities during peak daytime heating
hours and remain well-hydrated, particularly over the weekend.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 315 AM AST Thu Sep 17 2026

To start the next week, lingering tropical moisture will continue
over the islands under an east-southeast steering flow. Precipitable
water (PWAT) values will start at around 2 to 2.25 inches, high-end
normal to above normal values for this time of the year, before
becoming more spotty as patches of drier air filter in from Thursday
onwards. Throughout the period, areas of low pressure and surface
high pressure will move into the western Atlantic, sustaining a
generally light to moderate east-southeast steering flow.  An upper-
level low to the northeast will be present to start the week and
will continue to move southward and approach the islands. Current
model guidance suggests that this system will be east and northeast
of the islands by early next workweek and last through the long term
period. As of the latest guidance, 500 mb temperatures are forecast
at around -6 degrees Celsius while available moisture reaches the
upper levels through at least midweek, before retreating to the mid
levels. Uncertainty remains regarding this and the available
moisture reaching the islands midweek onwards. Please continue to
monitor the forecast for future updates. Light to moderate east-
southeasterly winds will steer ongoing showers toward windward
eastern areas, primarily during nighttime and morning hours. The
positioning of an upper-level low to the east and southeast brings
the potential for thunderstorm activity alongside these showers. In
the afternoons,  shower and thunderstorm development is forecast
across interior and western Puerto Rico, as well as downwind of El
Yunque, Vieques, Culebra, and the US Virgin Islands. Light to
moderate steering flow will allow rainfall to linger, also
maintaining a risk of flooding, particularly during the afternoon
hours across interior to western Puerto Rico. Additionally,
persistent moisture combined with the east-southeast wind flow may
result in limited to elevated heat risks.

&&

.AVIATION...
(18Z TAFS)
Issued at 148 PM AST Thu Sep 17 2026

Mostly VFR conds expected through the period. However, SHRA/TSRA
will continue to affect PR terminals this aftn, with brief MVFR/IFR
psbl at TJPS/TJBQ in heavier TSRA. VCSH expected across USVI
terminals. E-SE winds 15-20 kt with gusts 20-25 kt, bcmg 5-10 kt aft
23Z. E winds increase again aft 17/13-16Z.

&&

.MARINE...
Issued at 148 PM AST Thu Sep 17 2026

A departing tropical wave will continue to bring showers and
thunderstorms through the afternoon, with gusty winds, lightning,
and slightly reduced visibility, creating localized hazardous
conditions for small craft. A surface high pressure building over
the western Atlantic will then dominate the regional weather
pattern, leading to gentle to moderate east-southeasterly winds for
the next few days.

&&

.BEACH FORECAST...
Issued at 148 PM AST Thu Sep 17 2026

No changes were introduced to the beach forecast, with a moderate
risk of rip currents along exposed beaches of Puerto Rico and the
U.S. Virgin Islands. When visiting a beach under a moderate risk,
beachgoers must exercise caution as life-threatening rip currents
are possible along the surf zone. As winds are forecast to weaken,
the risk should become lower during the weekend, though beachgoers
should still pay attention to the beach conditions as isolated life-
threatening rip currents often occur near piers, groins, reefs, and
jetties. The low risk should continue over the next few days,
becoming moderate as winds strengthen by Tuesday. Aside from rip
currents, showers and isolated thunderstorms can be expected each
day, particularly in the afternoon, near the western/northwestern
coastal areas of Puerto Rico. These thunderstorms can include gusty
winds and lightning, becoming hazardous for beachgoers; they must
seek for shelter whenever they hear thunder.

&&

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

$$

SHORT TERM...JCP/CVB
LONG TERM...CAM/LIS/KML
KEY MESSAGES/AVIATION...CVB
MARINE/BEACH FORECAST...MNG