836
FXCA62 TJSJ 141859
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
259 PM AST Mon Sep 14 2026

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

.KEY MESSAGES...
Issued at 250 PM AST Mon Sep 14 2026

- An upper level low west-northwest of Puerto Rico will continue
  to favor the development of afternoon showers and t-storms over
  the region through tomorrow, especially late tomorrow morning
  and tomorrow afternoon.

- A tropical wave is expected to reach the region by Wednesday
  night increasing the potential for the development of deep
  convection into Thursday. This will elevate the flood risk in
  general across the islands.

- An elevated heat risk is possible tomorrow and is forecasted on
  Wednesday.

- A moderate risk of rip currents continues tonight and tomorrow
  for the north-facing beaches of PR; a low risk will persist
  elsewhere.

&&

.Short Term(This evening through Wednesday)...
Issued at 250 PM AST Mon Sep 14 2026

Shower and thunderstorm activity is being observed across the
islands since late this morning. Accumulations near 2 inches have
been observed over Vega Baja, Anasco, Aguada and Rincon. The
instability provided by the upper- level low combined with diurnal
heating, local orographic effects and sea breeze convergence will
continue to provide favorable conditions to promote showers and
isolated thunderstorms this afternoon over the islands, mainly over
interior towards western PR. The presence of the aforementioned
synoptic feature in our vicinity and a low-level surge in tropical
moisture passing south of the local area, will provide a similar
weather pattern for tomorrow. PWAT values will remain over
seasonal values (1.75 - 2.20 inches). Accumulations from this
anticipated activity, may lead to the ponding of water in roadways
and in poorly drained areas, as well as urban and small streams
flooding.

A drier air mass in the mid-levels (700-500 mb) is expected to
approach the region on Wednesday morning dropping PWAT values down
to 1.4 inches. This may limit shower and thunderstorm activity,
however local effects could still favor isolated shower and
thunderstorm activity, especially over the interior and western
PR. These drier conditions will be brief. A vigorous tropical wave
is forecast to reach PR and the U.S. Virgin Islands by Wednesday
evening into the long term period.

The heat risk for today remains limited. This level of heat
affects primarily those individuals with extreme sensitivity to
heat, especially when outdoors without effective cooling and/or
adequate hydration. The heat risk could increase on Tuesday and is
forecast to increase on Wednesday to an elevated level with
possible impacts to some health systems and in heat-sensitive
industries.

&&

.Long Term(Thursday through next Sunday)...
Issued at 240 AM AST Mon Sep 14 2026

The long-term forecast remains on track, with the highest flooding
threat on Thursday. As mentioned in the previous discussion, a
surface high pressure over the Central Atlantic should maintain an E-
SE wind flow throughout the forecast period, weakening by the next
weekend. The latest model guidance suggests abundant tropical
moisture associated with a tropical wave moving across the CWA, with
PWAT values above seasonal values (most likely between 2.0 - 2.2
inches, medium chance of reaching 2.4 inches). Additionally, the
soundings are tending to be skinny, with low-and mid-level
moisture higher than usual (up to 70 and 80%). Although a mid-to-
high-level ridge is in the vicinity, model guidance still suggests
areas of enhanced vorticity across the CWA, particularly early
Thursday. The most likely scenario remains the same, with showers
and isolated thunderstorms moving across sections of the U.S.
Virgin Islands and eastern/southeastern Puerto Rico early in the
morning, followed by afternoon convection across western/northwestern
Puerto Rico if cloud cover allows it. Mainly fair weather is
expected on Friday, as the latest NASA AOT model suggests a SAL
reaching the CWA, with a dry slot in the H8 - H7 level. Although
local effects and daytime heating can enhance convection, it
should remain limited. As the Saharan dust concentrations depart
the local area, Saturday and Sunday should have a seasonal weather
pattern, as an area of moisture arrives across the area, with
PWAT values between 1.8 and 2.0 inches. In the high levels, an
upper-level trough is likely to approach the eastern Caribbean,
weakening the ridge and introducing instability. With weakening
winds, afternoon convection may linger more in the mountain ranges
of Puerto Rico, increasing flood potential.

Once again, afternoon showers and thunderstorms are still forecast
each day, with most of the activity across interior and
western/northwestern Puerto Rico on Thursday and Friday, while
Saturday and Sunday should remain across interior Puerto Rico. As
mentioned above, Thursday has the highest flooding potential, with
urban and small stream flooding across interior and northwestern
Puerto Rico and minor flooding across the U.S. Virgin Islands and
eastern/southeastern Puerto Rico.

Seasonal warmer conditions are expected in the long-term, with the
hottest period by next weekend. Urban and low-lying areas can
expect maximum temperatures in the upper 80s and low 90s, with
heat indices above 100 F, affecting sensitive groups. The heat
threat will remain elevated throughout most of the forecast
period.

&&

.AVIATION...
(18Z TAFS)
Issued at 250 PM AST Mon Sep 14 2026

Mainly VFR conditions to prevail thru the period. -SHRA/TSRA will
continue to develop and/or move over the region and can reach the
terminals or their VCTY thru 14/18-22Z. Brief MVFR condtions
possible mainly over PR terminals at this time. VCSH possible over
eastern terminals thru the period. East winds 10 to 18 kt with
sea breeze variations and stronger gusts at times expected thru
14/22z, bcmg light and VRB thereafter. Winds increasing again to
12 to 18 kt with sea breeze variations and stronger gusts aft
15/13Z.

&&

.MARINE...
Issued at 250 PM AST Mon Sep 14 2026

A broad surface high pressure over the western Atlantic and a few
induced surface troughs will continue to result in moderate
easterly winds across the region. Under this pattern, seas will
remain under 5 feet with winds up to 15 knots. By late Wednesday
into Thursday, a tropical wave is forecast to approach the eastern
Caribbean, bringing an increase in showers and thunderstorms.
Conditions should gradually improve on Friday as the wave moves
west of the local area, while moderate easterly trades will
persist.

&&

.BEACH FORECAST...
Issued at 250 PM AST Mon Sep 14 2026

There is a moderate risk of rip currents across all northern and
northeastern coastal areas of Puerto Rico. The rest of the area
will remain at a low risk of rip currents, including west and
south Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands.
The rip current pattern is forecast to remain similar on Tuesday,
diminishing to low on Wednesday across all coastal areas. By
Wednesday into Thursday, a tropical wave is forecast to move
across the area, increasing the potential for showers and
thunderstorms across most of the islands. Therefore, beachgoers
should also remain alert for thunderstorms from Wednesday into
Thursday, as lightning, locally heavy rainfall, and gusty winds
may produce rapidly changing conditions near the coast. If thunder
is heard, leave the beach and seek safe shelter immediately.

&&

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

$$

SHORT TERM...JCP
KEY MESSAGES/AVIATION...MRR
LONG TERM....MNG
MARINE/BEACH FORECAST...LIS