textproduct: San Juan

KEY MESSAGES

Issued at 305 AM AST Thu Oct 15 2026

- An elevated flooding threat is expected across southwestern Puerto Rico today due to afternoon showers, with localized ponding of water in roadways and low-lying areas.

- For the U.S. Virgin Islands, limited shower activity is expected, with brief passing showers affecting mainly windward areas.

- Heat indices around 102 and 107 degrees Fahrenheit will pose a risk to outdoor workers and vulnerable populations after 10 AM everyday, when mostly clear skies prevail.

- A moderate risk of rip currents will persist along north exposed beaches of Puerto Rico and Culebra.

Short Term(Today through Saturday)

Issued at 305 AM AST Thu Oct 15 2026

A variable weather pattern prevailed overnight into the early morning hours across the local islands. Recent satellite imagery showed patches of cloudiness moving from the Atlantic waters into the region. Low-level cold-air advection, associated with cooler air moving over the relatively warmer Atlantic waters, enhanced low-level instability and supported the development of brief, passing showers. These showers moved across the local waters, with some reaching northeastern Puerto Rico and portions of the U.S. Virgin Islands. Shower activity remained generally light, resulting in minimal rainfall accumulations. Overnight temperatures ranged from the lower to mid-80s across urban and coastal areas, while temperatures across the mountainous regions remained in the upper 60s to lower 70s.

For today, surface conditions will be primarily influenced by a surface high-pressure system over the western Atlantic, which will maintain east to east-northeast winds across the region. Under this pattern, patches of low-level moisture, with precipitable water values remaining near climatological normals, will provide sufficient moisture to support limited passing showers across the U.S. Virgin Islands and windward sections of Puerto Rico during the morning hours. By midday, daytime heating, sea-breeze convergence, and orographic lifting will support afternoon convection across the western interior and southwestern municipalities of Puerto Rico. However, the latest GFS guidance indicates increasing mid-level stability, with 500 mb temperatures warming toward -4C and 700500 mb lapse rates decreasing throughout the period. These conditions will limit convective depth and overall thunderstorm development, although localized rainfall accumulations between 1.00 and 2.50 inches remain possible based on ensemble guidance. Consequently, an elevated flooding threat will persist across southwestern Puerto Rico, particularly where repeated showers affect the same areas. Elsewhere, significant rainfall accumulations are not anticipated.

A drier and more stable weather pattern will develop on Friday and persist into Saturday as a broad mid- to upper-level ridge remains established across the region. The latest GFS guidance suggests precipitable water values will generally decrease to around 1.501.80 inches on Friday, followed by a brief minimum near 1.30 inches early Saturday. Relative humidity within the 700500 mb layer will decrease, while 500 mb temperatures remain anomalously warm, near -4C. The combination of subsidence, mid-level warming, and reduced moisture availability will limit convective depth and shower coverage, favoring mostly sunny to partly cloudy skies across the local islands. Meanwhile, low-level winds at 925 mb will generally range between 10 and 15 knots, supporting the continued transport of shallow moisture patches embedded within the trade winds. Therefore, brief passing showers across windward areas and isolated afternoon showers over western Puerto Rico will remain possible, although widespread convective activity is not anticipated. A modest recovery in moisture later Saturday may support a slight increase in shower coverage across the region.

Long Term(Sunday through Thursday)

Issued at 305 AM AST Thu Oct 15 2026

The long-term forecast remains on track, with primarily stable weather conditions expected Sunday through early next week, followed by more active afternoons and slow-moving showers and thunderstorms by midweek.

A mid-to upper-level ridge will maintain dry and stable conditions aloft through Tuesday. Precipitable water (PWAT) will remain below- seasonal levels, ranging from 1.5 to 1.7 inches. Easterly steering winds will persist as low-level surface high pressure and a frontal boundary remain north of the local area. Passing cloud patches and trade wind showers will reach eastern sections of the islands (including the U.S. Virgin Islands) from time to time, with no significant impacts. Diurnal heating and local effects will still favor the development of afternoon showers and isolated thunderstorms across the interior to western sections of Puerto Rico, as well as downwind from El Yunque toward the southern half of the San Juan metropolitan area, and downwind from the USVI, Vieques, and Culebra. A limited flood threat will remain present each afternoon across interior to western Puerto Rico.

By the end of the day on Tuesday, the mid-level ridge will gradually dissipate. In its place, a mid-to-upper level trough will begin to cool the mid-levels and bring the lapse rates up to seasonal values, potentially enhancing the development of deep convection by Wednesday into Thursday. The steering flow will also experience a gradual weakening, especially by Wednesday, as the interaction between a surface-level trough and ridge to the north of the CWA leads to the collapse of the winds down to approximately 5 kts. By Tuesday, the direction of the steering flow will gradually shift to be from E to SE into the afternoon. This SE to S pattern will persist into the remainder of the long term period. The precipitable water values and column relative humidity will range between below to around seasonal levels on Tuesday and Wednesday and gradually increase into the afternoon on Thursday. The convective activity that develops each day will thus be driven by local effects, available moisture, and steering flow strength and direction. Rainfall may be expected to develop each day across the CWA and particularly affect the northern interior, interior, northwest, and northeast sectors of Puerto Rico. Advective showers may also develop and impact portions of the US Virgin Islands and southeastern Puerto Rico during the mornings and overnight hours.

A limited heat threat remains favored throughout the long-term period. While widespread heat hazards are not anticipated, extremely sensitive individuals could be affected and should take appropriate precautions to protect themselves from heat-related stress.

AVIATION

(06Z TAFS) Issued at 305 AM AST Thu Oct 15 2026

VFR conds will prevail across most local terminals through the fcst period. Brief SHRA will remain possible across TJSJ and USVI terminals during the morning hours. By 15/16Z, SHRA development is expected across the interior and SW PR due to diurnal heating and local effects, with brief MVFR conds possible near TJPS and TJBQ. Winds will prevail from the E to ENE at 10-15 kt with occasional higher gusts and sea-breeze variations.

MARINE

Issued at 305 AM AST Thu Oct 15 2026

Generally favorable marine conditions are expected through the end of the workweek, with light to moderate easterly winds and relatively tranquil seas. However, afternoon showers and isolated thunderstorms may produce locally hazardous conditions, particularly across the western and coastal waters of Puerto Rico. A lingering northeasterly swell will gradually subside through Friday, followed by another long-period northeasterly swell arriving over the weekend, resulting in increasing seas across the Atlantic waters.

BEACH FORECAST

Issued at 305 AM AST Thu Oct 15 2026

A moderate risk of rip currents will continue today along the beaches of San Juan and vicinity, north-central Puerto Rico, and Culebra, with a low risk elsewhere, including the U.S. Virgin Islands. The risk will decrease to low across all beaches Friday before potentially increasing again over the weekend as another long- period northeasterly swell reaches the region. Afternoon showers and isolated thunderstorms may also pose a lightning threat to beachgoers, particularly across western and southwestern Puerto Rico, with improving conditions expected Friday.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.