textproduct: San Juan

KEY MESSAGES

Issued at 353 AM AST Mon Oct 26 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, particularly in coastal and urban areas. Elevated heat impacts will persist Tuesday before easing Wednesday.

* Life-threatening rip currents will affect exposed beaches through Wednesday, particularly along northern, northwestern, and eastern Puerto Rico, Culebra, and portions of the northern U.S. Virgin Islands. Today will be the peak event with also a High Surf Advisory in effect for the northwestern and northern coastline of Puerto Rico through late tonight.

* Repeated showers this afternoon and tonight could produce urban and small stream flooding and isolated flash flooding across southern Puerto Rico. A more limited flooding threat will affect eastern Puerto Rico and the southern slopes, with isolated thunderstorms bringing lightning and gusty winds.

* Hazardous seas will also affect small craft today and Tuesday. Rainfall coverage should decrease Wednesday and Thursday as drier air arrives.

* The ECMWF indicates greater drying than the GFS, limiting confidence in how much the pattern improves. Increasing moisture and cooler temperatures aloft could support renewed heavy showers and thunderstorms Friday into Saturday, increasing the potential for localized flooding.

Short Term(Today through Wednesday)

Issued at 353 AM AST Mon Oct 26 2026

Mostly clear to partly cloudy skies prevailed overnight. Temperatures stayed above typical October lows across much of the region, with readings since midnight generally in the lower to mid-80s in coastal and urban areas and the U.S. Virgin Islands, and in interior Puerto Rico in the mid-60s to 70s. Southerly flow carried showers from the local waters into windward areas, mainly along southern Puerto Rico, producing periods of moderate to locally heavy rainfall.

The unusually warm start will cause temperatures to rise quickly this morning, with hot, humid conditions increasing the risk of heat-related illness, particularly across coastal and urban areas of Puerto Rico and the U.S. Virgin Islands. A Heat Advisory is in effect for the region. Southeasterly flow will carry showers into windward areas today and tonight as moisture increases. The flooding threat will be greatest across southern Puerto Rico, where persistent or repeated showers could produce urban and small stream flooding and isolated flash flooding. Elsewhere across southern slopes and eastern Puerto Rico, heavier showers could cause ponding on roads and in poorly drained areas. A ridge at mid and upper levels, warm temperatures aloft, and relatively dry mid-levels will limit deep convection. Nevertheless, daytime heating, sea breeze convergence, and terrain effects will support isolated afternoon thunderstorms, bringing lightning and brief gusty winds.

Puerto Rico and the U.S. Virgin Islands will remain between a trough over the western Caribbean and a ridge over the eastern Caribbean through Tuesday. Southerly to southeasterly flow will transport tropical moisture across the region, while warm surrounding waters help maintain a moist boundary layer. Local convergence, daytime heating, and terrain effects will support additional rounds of showers, particularly Tuesday afternoon into the overnight hours. The flooding threat will remain limited, with heavier or repeated showers producing ponding on roads and in poorly drained areas, as well as isolated urban and small-stream flooding, mainly across eastern and northwestern Puerto Rico and portions of Vieques.

On Wednesday, both GFS and ECMWF guidance indicate decreasing moisture, although they differ on the extent of drying. The GFS keeps precipitable water near 1.8 to 2.0 inches, while the ECMWF lowers it to 1.3 to 1.5 inches, below typical October values. Both models maintain warm temperatures aloft and relatively weak lapse rates, limiting widespread thunderstorms. Lingering moisture and local convergence will still support localized showers, but the ECMWF solution would favor substantially less rainfall. Above- normal temperatures at low levels will keep conditions warm and humid, particularly across coastal and urban areas.

Above-normal temperatures and humid conditions will keep heat risk elevated Tuesday, particularly across coastal and urban areas. Some relief is expected Wednesday as drier air arrives, although heat-sensitive individuals and those outdoors without adequate cooling or hydration will remain at risk.

Long Term(Thursday through Monday)

Issued at 353 AM AST Mon Oct 26 2026

No major changes were introduced to the long-term forecast, as wetter and more unstable conditions continue to be forecast this weekend. The latest model guidance continues to suggest a surface high pressure over the Central Atlantic interacting with a polar trough deepening into the tropics, maintaining an ESE-SE wind flow throughout the forecast period. A mid-to-upper level ridge northeast of the CWA should continue to dominate the weather pattern on Thursday, as guidance suggests warmer-than-normal 500 mb temperatures (above -6 C) and low mid level lapse rates, indicating unfavorable conditions for deep convection. Additionally, the Galvez- Davison Index (GDI) suggests shallow convection on Thursday afternoon across the mountain ranges of Puerto Rico. As mentioned in the previous discussions, PWAT values should remain below climatological normal (below 1.75 inches), with the dry slot in the low and mid levels. Although daytime heating combined with local effects and sea breeze convergence should aid in breaking the cap inversion and allow shower and thunderstorm activity, rainfall accumulations should remain minimal.

Friday onwards, global models continue to suggest wetter and unstable conditions across the CWA, as the trough approached the CWA, weakening the ridge, leading to divergence aloft and enhancing instability. Additionally, the latest NCICS forecast continues to suggest the Madden-Julian Oscillation (MJO) over the CWA, which may enhance upward motion and divergence aloft. The latest deterministic guidance from the GFS and ECMWF suggests PWAT values could reach up to 2.25 inches, slightly above normal, mainly in the low and mid levels. Additionally, the guidance suggests skinny-sounding profiles, with high CAPEs, and cooler- than-normal mid-level temperatures (between -6 and -8 C), and stronger upper- winds, allowing cloud growth and ventilation. Therefore, the most likely scenario remains, with an advective pattern across windward sections of the islands early Saturday, followed by deep afternoon convection across mountain ranges of Puerto Rico, including the San Juan Metro Area. Rainfall accumulations could lead to urban and small stream flooding, without ruling out flash flooding. Additionally, rivers may rise quickly. Therefore, the flood threat will remain limited to elevated across the aforementioned areas on Friday, Saturday, and Sunday. Besides flooding, thunderstorms could produce gusty winds and frequent lightning.

AVIATION

(06Z TAFS) Issued at 353 AM AST Mon Oct 26 2026

Mainly VFR conditions will prevail outside SHRA/TSRA. SE flow will carry SHRA across USVI and southern and eastern PR terminals today and tonight. Heavier SHRA may produce brief MVFR conditions and mountain obscuration btwn 26/15-22z. Local convergence may support isolated afternoon TSRA across PR. Isolated TSRA could bring lightning, gusty winds, and locally reduced visibility. SE winds will prevail at 5-15kt, with daytime sea breeze variations and higher gusts near SHRA.

MARINE

Issued at 353 AM AST Mon Oct 26 2026

A surface high pressure over the central Atlantic will promote moderate to locally fresh east to southeasterly winds across the region through midweek. A long period northerly swell is expected to spread across the Atlantic waters and passages today, building seas between 6 to 8 feet through Tuesday. Small craft advisories will be in effect for the Atlantic waters and the Mona Passage starting later today. Isolated thunderstorms are expected to develop mainly over the Caribbean waters, the Mona Passage, and offshore Atlantic waters during the next few days.

BEACH FORECAST

Issued at 353 AM AST Mon Oct 26 2026

A long period northerly swell will arrive today, with additional pulses expected through midweek. This swell could generate breaking waves between 6 and 12 feet, that will cause rough surf and life- threatening rip currents, mainly along the north facing beaches of Puerto Rico, Culebra, and the northern U.S. Virgin Islands. A High Rip Current Risk is in effect for the northern, western, and eastern beaches of PR and Culebra through at least Tuesday. High surf advisory is also in effect for the northwestern and northern coastline of Puerto Rico through late tonight. Beachgoers are strongly urged to avoid entering the water at beaches under these Advisories. Heed all beach signs/flags 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.

High Surf Advisory until 6 AM AST Tuesday for PRZ001-002-005-008- 010.

Heat Advisory until 5 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...Small Craft Advisory from noon today to 6 PM AST Tuesday for AMZ711.

Small Craft Advisory from 6 PM this evening to 6 PM AST Tuesday for AMZ712-741-742.