textproduct: San Juan

KEY MESSAGES

Issued at 421 AM AST Sun Oct 25 2026

* A Heat Advisory is in effect today for Puerto Rico and the U.S. Virgin Islands. Hot, humid conditions will increase the risk of heat-related illness, especially in urban and low-lying areas and with prolonged outdoor exposure.

* Persistent showers and isolated thunderstorms this afternoon, early evening, and again late tonight into early Monday could produce urban and small-stream flooding and rapid river rises, particularly across southern and eastern Puerto Rico.

* Life-threatening rip currents will affect exposed northern, northwestern, and eastern beaches of Puerto Rico, and Culebra today and tonight. Moderate risk will persist across Vieques and the U.S. Virgin Islands.

* Rainfall coverage should decrease Monday, while moisture guidance differences limit confidence in Tuesday's flooding potential. Warm, humid conditions will keep heat concerns through the period.

* Drier conditions Wednesday and Thursday will give way to increasing moisture and instability Friday into Saturday. Persistent thunderstorms could renew localized flooding concerns and produce lightning and gusty winds.

Short Term(Today through Tuesday)

Issued at 421 AM AST Sun Oct 25 2026

A mid- to upper-level trough over the western Caribbean and a ridge aloft over the eastern Caribbean, combined with southeasterly surface flow, maintained a moist environment across the region overnight. Showers developed over the waters surrounding Puerto Rico and the U.S. Virgin Islands and occasionally moved inland across windward areas. Temperatures remained above normal, with partly cloudy to mostly clear skies over the islands and greater cloud cover over the Mona Passage.

Sunday has begun warmer than normal. Combined with abundant humidity and recent heat indices between 100 and 110 degrees Fahrenheit, this supports another day of hazardous heat. A Heat Advisory is in effect for Puerto Rico and the U.S. Virgin Islands, with the greatest impacts in urban and low-lying areas. Prolonged outdoor exposure without adequate hydration or effective cooling increases the risk of heat-related illness.

The 25/00Z San Juan sounding sampled precipitable water near 2.0 inches and sufficient instability for thunderstorms, although a stable layer near 680 mb could limit convective depth. Southeasterly flow and abundant tropical moisture will support periods of persistent showers this afternoon and early evening, followed by additional rounds late tonight into early Monday. Rainfall guidance differs on where heavier activity will fall, with concern across southern and eastern Puerto Rico and localized afternoon development farther inland and west. Repeated showers could produce urban and small stream flooding and rapid river rises. Although we do not anticipate scattered thunderstorms, a few of them could bring lightning and brief gusty winds.

Both GFS and ECMWF guidance favor decreasing moisture depth, warming aloft, and reduced rainfall coverage Monday. However, lingering moisture will support showers and localized afternoon thunderstorms as they pass through. Tuesday remains more uncertain, as the GFS restores precipitable water toward 2.0 inches while the ECMWF keeps it drier, near 1.4 to 1.6 inches. The wetter solution would support renewed heavy rainfall and localized flooding.

Above-normal temperatures near 925 mb support continued warm, humid conditions through Tuesday, maintaining heat concerns, especially across urban and low-lying areas.

Long Term(Wednesday through Sunday)

Issued at 421 AM AST Sun Oct 25 2026

Fair weather conditions should continue over the second part of the workweek, becoming wetter and unstable by the weekend. A surface high pressure over the central Atlantic should continue to maintain a SE-S wind flow through most of the forecast period. However, the steering flow should remain weak as the surface high interacts with a deep-layered trough deepening into the tropics, weakening the local pressure gradient.

Aloft, global model solutions continue to suggest a ridge in the central Atlantic interacting with the trough, though the ridge should continue to dominate the weather pattern on Wednesday and Thursday. During this period, guidance suggests a drop in moisture content across the CWA, with PWAT values below climatological normal (below 1.75 inches), as a dry slot filter in the low and mid levels. Additionally, the vicinity of the ridge will likely maintain warmer-than-normal mid level temperatures (above 6 C), leading to subsidence and stability aloft.

According to the latest CFS forecast, the CWA may be under a suppressing area, disfavoring deep convection. Although daytime heating and local effects will drive the afternoon convection, showers and isolated thunderstorms over the mountain ranges of Puerto Rico may not produce significant rainfall, lowering the flood chance. Friday onwards, the weather conditions may become wetter and unstable as the deep- layered trough and a TUTT approaches the local area, cooling mid level temperatures (between -6 and -8 C), with steeper mid-level lapse rates, increasing instability aloft. Additionally, CFS forecasts the MJO across the local area, enhancing upward motion and favoring deeper convection. Additionally, PWAT values should reach above-normal values (up to 2.25 inches), reflected in both low and mid levels, reflected in the latest deterministic guidance of the GFS and ECMWF.

Additional to afternoon convection across Puerto Rico, showers and isolated thunderstorms may move across windward sections of Puerto Rico and the U.S. Virgin Islands during the night and morning hours, followed by afternoon convection across the mountain ranges of Puerto Rico. Due to low steering winds, showers and thunderstorms may linger longer than usual, increasing rainfall accumulations over the aforementioned areas. Therefore, the flood threat will remain elevated on Friday and Saturday, with mainly urban and small stream flooding, along with rapid river rises. Thunderstorms may produce gusty winds and frequent lightning.

AVIATION

(06Z TAFS) Issued at 421 AM AST Sun Oct 25 2026

Mainly VFR conditions will prevail outside SHRA/TSRA. Passing SHRA will affect eastern/southern PR and USVI terminals this morning. Afternoon convection may produce brief MVFR conditions and mountain obscuration across PR. Additional SHRA will affect southern and eastern terminals tonight into early Monday. TSRA may produce lightning, gusty winds, and locally lower visibility. SE winds around 10 kt will prevail, with sea breeze variations and higher gusts near convection.

MARINE

Issued at 421 AM AST Sun Oct 25 2026

A surface high pressure over the central Atlantic will promote moderate to locally fresh southeasterly winds across the region through at least Tuesday. Choppy seas are expected to continue across the Atlantic waters and the Mona Passage today. A long period northerly swell is expected to spread across the Atlantic waters and passages by Monday, building seas once again up to around 7 feet and maintaining hazardous conditions through at least Tuesday.

BEACH FORECAST

Issued at 421 AM AST Sun Oct 25 2026

A subsiding northerly swell and additional pulses of long period northerly swells will cause life threatening rip currents along the north facing beaches of Puerto Rico and Culebra through early in the week. Therefore, a High Rip Current Risk continues in effect for the northern, western, and eastern beaches of PR and Culebra through at least Tuesday. Beachgoers are strongly urged to avoid entering the water at beaches under a high rip current risk. Heed all beach signs and instructions from lifeguards and local authorities.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Tuesday afternoon for PRZ001-002- 005-008-010-012.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ001-002.

AM...None.