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331
FXCA62 TJSJ 031717
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
117 PM AST Tue Nov 3 2026

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

.KEY MESSAGES...
Issued at 107 PM AST Tue Nov 3 2026

- Warmer and humid conditions continue today, particularly across
  urban and low-lying areas of the islands. Therefore, the Heat
  Advisory is now in effect through 4 PM AST.

- For the rest of the afternoon, showers and isolated
  thunderstorms are expected across the interior, western, and
  northwestern Puerto Rico, leading to ponding of water over
  roadways and minor flooding.

- A wetter pattern is expected from Thursday through Saturday.
  Increasing moisture and slow-moving showers and thunderstorms
  could raise the flooding threat, including urban and small-
  stream flooding, with isolated flash flooding possible.

- Another swell is forecast to arrive this Friday into the
  weekend, bringing hazardous seas and life-threatening rip
  currents. Refer to the Beach Forecast section for additional
  details.


&&

.Short Term(This evening through Thursday)...
Issued at 107 PM AST Tue Nov 3 2026

Abundant low-level tropical moisture remains entrenched mainly
across the Caribbean Sea, with precipitable water (PWAT) values just
over 2.00 inches. However, recent upper air data show lingering mid-
level dryness, keeping convective development somewhat localized
today. With light south-southeasterly low-level steering flow below
10 knots, intense solar heating will interact with sea breeze
convergence and local topography to trigger scattered afternoon
showers and isolated thunderstorms mainly across the interior,
western, and northwestern sections of Puerto Rico. Across the U.S.
Virgin Islands and eastern Puerto Rico, isolated passing trade wind
showers will produce minimal accumulations, allowing temperatures to
rise into the upper 80s to low 90s, with heat indices increasing to
near 108F. A heat advisory remains in effect until 4 PM this
afternoon.

By Wednesday, in response to a developing surface low pressure from
a frontal boundary well north of the region, moisture content will
gradually increase as winds shift more southerly, pulling the moist
tropical air northward into the region. Aerosol models indicate a
surge of minor concentrations of suspended Saharan dust filtering
into the region, contributing to hazy skies. However, steady erosion
of mid-level dry air and rising instability indices will favor more
widespread convective initiation than today. PWAT will increase
above climo, up to around 2.25 inches. Weak southeasterly steering
winds will maintain primary convergence over the Cordillera Central
and the northern and western slopes of Puerto Rico during the
afternoon. Strong daytime insolation, steep low-level lapse rates,
and favorable convective instability will support strong
thunderstorm development capable of producing heavy rainfall,
frequent lightning, and gusty winds. Consequently, the potential for
urban and small-stream flooding will increase significantly due to
the expected slow-moving showers.

Thursday will be the most active day in the short term, as deep-
layer moisture pooling and strong low-to mid-level moisture flux
convergence overspread the region. Tropical moisture embedded in a
deep southwesterly wind flow will support scattered showers and
isolated thunderstorms across the regional waters and coastal areas
of PR during the morning, followed by widespread, intense afternoon
convection across the interior and northern and eastern quadrants of
PR. With continued weak steering and persistent cell training, the
threat of urban and small-stream flooding, localized flash flooding,
and landslides in steep terrain will increase.

&&

.Long Term(Friday through Tuesday)...
Issued at 257 AM AST Tue Nov 3 2026

For Friday through Saturday, atmospheric instability is expected to
remain elevated. Precipitable water (PWAT) values will continue
above normal (between 2 to 2.3 inches) through at least Sunday.
Relative humidity (RH) in the 850700 mb layer will stay high while
mid-level moisture (700500 mb) is set to increase to 80% through
early Saturday.  An upper-level trough, along with its corresponding
surface low and frontal boundary, will track northward across the
Atlantic. Although the core of maximum instability is expected to
pass north of the area, this will set up a southwesterly to westerly
(light to variable) steering flow, drawing tropical moisture
northward into our area. This steering flow will be generally light
and variable. Consequently, slow-moving showers are likely to
develop, generating elevated rainfall totals, primarily across the
southern, interior, northern and northeastern sectors of Puerto
Rico, as well as the U.S. Virgin Islands. This will result in
flooding (Risk level 2 of 4) especially across interior, northern
and northeastern Puerto Rico during the afternoon hours. Although
model guidance continues to indicate mid to upper level ridging
building over the islands to start the next week, prompting a more
stable pattern. Model discrepancies continue through Tuesday. The
GFS preserves higher moisture availability throughout the
atmospheric column, specifically within PWAT, 850700 mb RH and 700-
500 mb RH. Conversely, the ECMWF projects a drier 850-500 RH profile
alongside reduced PWAT values. Uncertainty continues to be present
concerning the overall moisture content. While daytime heating and
local effects can trigger isolated to scattered afternoon showers
across the islands, an overall reduction in rainfall coverage and
intensity is anticipated, thereby lowering the risk of flooding.
Steering flow Sunday through Tuesday is forecast to be generally
light to variable from the southwest before gradually backing and
becoming more southerly as the period continues. Please monitor
future updates as changes to the forecast are possible.

&&

.AVIATION...
(18Z TAFS)
Issued at 107 PM AST Tue Nov 3 2026

Mainly VFR conditions are expected to prevail across all terminals
through much of the forecast period. However, locally induced
afternoon SHRA/TSRA over the interior and NW PR may cause tempo MVFR
conds at TJBQ, while VCTS prevails at TJPS through 03/21Z. Mostly
VCSH expected across the rest of the PR and USVI terminals. The
03/12z TJSJ sounding indicated variable winds up to 6 kt blo 2500ft.
However, after 03/13z sfc winds acquired a SE component up to 12
kts, while a weak northerly sea breeze variations were observed
along the northern coast of PR and should diminish by 03/21z. HZ due
to suspended Saharan dust is expected through late Wednesday, but
VSBY should remain P6SM.

&&

.MARINE...
Issued at 107 PM AST Tue Nov 3 2026

A surface high pressure in the Western Atlantic will  continue to
maintain light to moderate east to southeast winds for the rest of
the afternoon and tonight. However, winds will gradually weaken and
become light from the south-southwest as a surface low develops
north of Puerto Rico and weakens the pressure gradient Wednesday
onward. Seas will generally subside through Friday, though the
arrival of a  north-northwesterly swell arrives Friday into the
weekend, building seas across the local Atlantic waters and
Caribbean passages, creating locally hazardous conditions for small
craft. Shower and thunderstorm activity is forecast to increase
across the regional waters on Thursday and Friday, bringing gusty
winds, slightly reduced visibility, and lightning.

&&

.BEACH FORECAST...
Issued at 107 PM AST Tue Nov 3 2026

The moderate risk of rip currents continues across northern and
eastern-exposed beaches of Puerto Rico, including Culebra, and the
U.S. Virgin Islands; low elsewhere. Beachgoers must exercise caution
while visiting beaches under moderate risk, as life-threatening
currents are possible along the surf zone. The risk should gradually
lower tonight through Friday, as the steering wind flow weakens,
though isolated rip currents could occur near jetties, piers, reefs,
and groins; beachgoers should pay attention to the beach conditions.
A high rip current risk is likely this weekend, as a north-
northwesterly long-period swell generated by the low pressure
developing well north of the region arrives by Friday. Based on the
latest model guidance, the swell could increase breaking waves and
lead to hazardous conditions for beachgoers, particularly on
Saturday and Sunday, across north-exposed beaches of the islands.
Residents and visitors should  continue to monitor the beach
conditions and stay up to date with the latest beach forecast. Aside
from rip currents, beachgoers should also pay attention to the
weather conditions, as showers and thunderstorms each afternoon
could move near coastal areas of the islands, increasing the
likelihood of lightning. Seek shelter whenever you hear thunder.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...DS
LONG TERM....MRR
MARINE/BEACH FORECAST...MNG

NWS SJU Office Area Forecast Discussion