Flash Flood Warning 29, NWS JSJ

019 
WGCA72 TJSJ 010713
FFSSJU

Flash Flood Statement
National Weather Service San Juan PR
313 AM AST Tue Sep 1 2026

PRC057-010723-
/O.EXP.TJSJ.FF.W.0029.000000T0000Z-260901T0715Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Guayama PR-
313 AM AST Tue Sep 1 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 315 AM AST EARLY THIS MORNING
FOR GUAYAMA COUNTY...

Flood waters have receded. The heavy rain has ended. Flooding is no
longer expected to pose a threat. Please continue to heed remaining
road closures.

&&

LAT...LON 1802 6620 1803 6617 1805 6617 1804 6613
      1809 6613 1810 6606 1806 6609 1803 6608
      1802 6609 1797 6607 1797 6609 1793 6615
      1794 6615 1793 6617 1795 6617 1795 6618
      1793 6621 1794 6620

$$

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Area Forecast Discussion
National Weather Service San Juan PR
250 PM AST Mon Aug 31 2026

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

.KEY MESSAGES...
Issued at 241 PM AST Mon Aug 31 2026

* Unsettled Weather: Periods of showers and thunderstorms will
  affect Puerto Rico and the U.S. Virgin Islands. Heavy rainfall
  could cause ponding and localized flooding in urban areas and
  small streams.

* High Rip Current Risk: Life-threatening rip currents will remain
  likely along north-and east-facing beaches of Puerto Rico and
  the U.S. Virgin Islands through this evening.

* Increasing Heat: Abundant moisture combined with hot
  temperatures will result in an elevated to high risk of extreme
  heat, particularly Tuesday and Wednesday.

* Beneficial rainfall ahead: Another tropical wave will increase
  rainfall chances during the second half of the workweek.
  Additional moisture early next week could bring further
  beneficial rainfall to the region.

&&

.Short Term(This evening through Wednesday)...
Issued at 241 PM AST Mon Aug 31 2026

The region was under a southeasterly wind flow today. Weather
stations along the windward sections reported prevailing winds
from the east to east-southeast at 15 to 25 mph, with a station at
Buck Island, St Thomas reporting sustained winds of 20 to 30 mph
with higher gusts. Maximum temperatures ranged from the upper 80s
to the low 90s across urban and coastal areas, with lower
temperatures in the mountains and valleys. Skies were mostly
cloudy along the eastern half of Puerto Rico and the US Virgin
Islands, while the western half of Puerto Rico observed mostly
sunny to partly cloudy skies. Thunderstorms developed along the
northwest quadrant early this afternoon. Some showers moved across
the US Virgin Islands and eastern PR from the east early this
afternoon. A record maximum temperatures of 94 degrees Fahrenheit
was tied at the San Juan Metropolitan area this afternoon.

An unstable weather pattern, fueled by abundant tropical moisture
from the trailing remnants of Dolly, will keep the chance of
showers and thunderstorms high across the region through at least
tomorrow, Tuesday. Thus, we expect brief periods of unsettled
weather for the US Virgin Islands and Puerto Rico through
tomorrow, with a limited to elevated risk of flooding, meaning
ponding in poorly drained areas and urban and small-stream
flooding is likely, without ruling out isolated flash flooding,
especially along the northwest quadrant of PR this afternoon.
Later this evening into the overnight, we expect additional
periods of showers and possibly isolated thunderstorms moving from
the waters into the USVI and eastern PR. Then, by Tuesday
afternoon, another round of convection is expected along the
interior and western PR, as well as downwind of the Luquillo
mountain range and downwind of St. Croix and St. Thomas.

A similar pattern is possible for Wednesday, but more seasonal, as
most trailing moisture will exit the region. However, available
moisture combined with local air temperatures will produce hot and
possibly dangerous heat indices. Afternoon convection will form
once again on Wednesday afternoon.

&&

.Long Term(Thursday through next Sunday)...
Issued at 333 AM AST Mon Aug 31 2026

A surface high pressure system over the western Atlantic,
interacting with another high over the central Atlantic, will remain
the dominant surface feature through the first part of the long-term
period. This setup will maintain an easterly wind flow across the
region from Thursday into Friday, some pockets of moisture embedded
in the easterly winds will move in and out of the forecast area.
Under this pattern, variable weather conditions are expected, with
periods of passing showers alternating with warm conditions and peak
heat indices ranging from 100 to 111 degrees. In the afternoon, sea
breeze convergence and local effects will combine with available
moisture to promote convective development across western sectors of
Puerto Rico, resulting in localized showers with a none-to-limited
flooding threat across western sections of the island.

On Friday, surface conditions will change as the central Atlantic
high expands southward into the Caribbean, inducing a south-
southeasterly wind flow that will drag moisture from an approaching
tropical wave into the forecast region. At the upper levels, a low
pressure system will increase instability across the area,
particularly during the late afternoon and evening hours. This
evolving pattern will boost precipitable water (PWAT) values up to
2.0 inches, tighten the local pressure gradient to increase surface
winds, and enhance cloudiness and shower potential across the
region. According to the GFS, moisture will arrive early Friday
morning and persist throughout the day; conversely, the ECMWF shows
a more northerly moisture trajectory. Nevertheless, both global
models agree on a similar outcome: an unstable and wet weather
regime for the end of the workweek. By Saturday, low-level winds
will remain from the southeast with sufficient low-level moisture in
place. However, a upper-level southerly wind flow will filter mid-
to upper-level clouds across the local islands for much of the day.
This persistent cloud cover may limit surface insolation and
slightly cap peak heat indices, though ambient temperatures will
still ramp up into the upper 80s to low 90s, maintaining warm
conditions and potential heat-related risks across lower elevations.

During the latter part of the long-term period from Sunday into
Monday, atmospheric moisture will increase further as another
tropical wave, lifting northward out of the Intertropical
Convergence Zone (ITCZ), tracks into the local forecast area.
Guidance suggests that the northern axis of this wave will interact
with the local island terrain and favorable low-level wind
convergence, pulling deep tropical moisture into the CWA and pushing
precipitable water (PWAT) values above seasonal normals. This
moisture increase will enhance cloudiness across the regional waters
and islands, resulting in widespread passing showers over coastal
areas during the overnight and morning hours. By the afternoon, the
combination of daytime heating, local effects, and sea breeze
convergence will significantly increase the potential for moderate
to heavy shower and thunderstorm activity across interior and
western sectors of Puerto Rico.

&&

.AVIATION...
(18Z TAFS)
Issued at 241 PM AST Mon Aug 31 2026

Moisture trailing the remnants of Dolly, mainly well west of the
region, will continue to support SHRA and TSRA and mid to upper
level cloudiness across the region thru the forecast prd. VCTS/TSRA
most likely to affect TJBQ/TJSJ thru around 31/21Z, but remains psbl
for other terminals. This TSRA can result in tempo MVFR/IFR conds.
SHRA will remain psbl for the terminals thru much of the prd. E-ESE
flow up to around 12 kt, with higher gusts, thru 31/23Z, decreasing
overnight and picking up again from the E-ESE after 01/12Z.

&&

.MARINE...
Issued at 241 PM AST Mon Aug 31 2026

Showers and thunderstorms associated with trailing moisture from
the remnants of Dolly will continue to redevelop across the
regional waters today. Periods of torrential rainfall, frequent
lightning, and strong gusty winds are possible with the strongest
thunderstorms. A Small Craft Advisory remains in effect for the
offshore Atlantic waters, where seas could reach up to 7 feet. A
weak surface high pressure building across the central Atlantic by
midweek will promote moderate easterly trade winds through much of
the workweek. The next tropical waves are forecast to reach the
local waters toward the end of the workweek and early next week,
bringing another increase in shower and thunderstorm activity.

&&

.BEACH FORECAST...
Issued at 241 PM AST Mon Aug 31 2026

A high risk of life-threatening rip currents will persist along
north- and east-facing beaches of Puerto Rico and the U.S. Virgin
Islands through this evening. The risk is expected to decrease to
moderate on Tuesday, then become low Wednesday and Thursday.

For St. Croix, the rip current risk should remain low through
much of the workweek before increasing to moderate during the
weekend.

Thunderstorms are also expected across the region. If you hear
thunder, seek safe shelter immediately and stay away from the
beach and open water.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for PRZ001>003-
     005-008-012-013.

VI...High Rip Current Risk until 6 PM AST this evening for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST this evening for AMZ711.

&&

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

Special Weather Statement
National Weather Service San Juan PR
1134 PM AST Mon Aug 31 2026

PRZ002>004-006-007-010500-
Eastern Interior PR-Central Interior PR-Northeast PR-Southeast PR-
Ponce and Vicinity PR-
1134 PM AST Mon Aug 31 2026

...A LINE OF SHOWERS WILL IMPACT SOUTHEASTERN MUNICIPALITIES UNTIL 1
AM AST...

At 1134 PM AST, Doppler radar was tracking a line of showers
extending from 5 miles southeast of Jauca to 6 miles southeast of
Humacao, or extending from 5 miles south of Salinas to 6 miles
southeast of Humacao, moving north at 25 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
  Guayama, Coamo, Santa Isabel, Cayey, Arroyo, Patillas, Aibonito,
  San Lorenzo, Salinas, Maunabo, Yabucoa, Juncos, Las Piedras,
  Humacao, Emajagua, Olimpo, Corazon, Buena Vista, Palmas and Jobos.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 1811 6649 1817 6606 1825 6583 1815 6576
      1806 6580 1805 6584 1801 6583 1793 6616
      1794 6615 1793 6621 1794 6617 1796 6621
      1794 6626 1793 6625 1798 6632 1794 6639
      1797 6643 1796 6643
TIME...MOT...LOC 0334Z 161DEG 22KT 1790 6632 1798 6596 1807 6578

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

YZR