textproduct: San Juan

KEY MESSAGES

Updated at 157 PM AST Thu Aug 27 2026

- Extreme Heat Primary Threat: Extreme heat remains the main hazard, especially across urban and coastal areas.

- Variable Moisture Pattern: Intermittent moisture patches will alternate with below-normal moisture during drier periods through Saturday.

- Active Afternoons: Afternoon showers and thunderstorms will remain active across portions of Puerto Rico, with locally heavy rainfall possible.

- Watching Dolly Sunday to Monday: Dolly is expected to weaken while approaching the northeastern Caribbean. Associated moisture may increase showers and thunderstorms, but impacts remain uncertain.

- Marine and Coastal Hazards Increase: Marine conditions and rip- current risks are expected to worsen late this weekend into early next week.

Short Term(This evening through Saturday)

Issued at 157 PM AST Thu Aug 27 2026

A drier and more stable air mass will spread across the region tonight as today's moisture moves west. Strengthening mid-level ridging and increasing subsidence will reinforce the trade-wind inversion, limiting shower development. Nevertheless, patches of low- level moisture embedded in the easterly flow will continue to support brief passing showers across windward areas overnight.

A variable moisture pattern will continue Friday into Saturday, with intermittent patches of moisture alternating with periods of below- normal moisture. Friday should feature the driest conditions, although passing morning showers and locally induced afternoon convection will remain possible. Shower and thunderstorm activity should become somewhat more active Saturday as an easterly disturbance and increasing moisture move across the region. Afternoon convection will favor the interior and western portions of Puerto Rico, where locally heavy downpours could result in ponding of water and localized flooding.

Extreme heat remains the primary hazard through the short-term period. Heat risk should decrease closer to normal levels Friday, before increasing above normal again Saturday. The highest heat impacts will continue to favor urban and coastal areas, particularly during periods of reduced cloud and shower coverage.

Mainly VFR thru the period. SHRA near PR terminals thru this evening, improving overnight. Aftn SHRA/iso TSRA mainly interior/wrn PR may cause brief MVFR and mtn obsc, especially near TJBQ. E winds 15-20 kt with higher gusts/sea-breeze variations, decreasing to 5-10 kt and VRB aft 27/23Z.

Long Term(Sunday through next Wednesday)

Issued at 157 PM AST Thu Aug 27 2026

Forecast uncertainty remains higher than usual heading into early next week, primarily associated with Tropical Storm Dolly, currently over the central tropical Atlantic. According to the latest Tropical Weather Outlook from the National Hurricane Center, the storm has become favorable for cyclonic development, though the system will likely remain short-lived as environmental conditions are expected to become less conducive for development this weekend. Nevertheless, the evolution of Dolly and its associated moisture field will continue to be monitored for potential impacts across Puerto Rico and the U.S. Virgin Islands.

The current forecast generally follows the timing depicted by the GFS and ECMWF, both of which indicate increasing moisture and precipitable water values from late Sunday through at least Tuesday. Although their timing is relatively similar, the GFS remains more aggressive with moisture and rainfall than the ECMWF. Part of this difference appears related to the evolution of the mid- level ridge. The ECMWF maintains stronger ridging closer to the northeastern Caribbean Sunday into Monday, which would favor greater subsidence and potentially disrupt the disturbance and its moisture field. In contrast, the GFS shifts the ridge farther west ahead of Dolly, allowing deeper moisture to approach the region.

Given these trends, the forecast favors a wetter pattern Sunday into Monday, with increasing shower and thunderstorm activity and a more widespread limited flooding risk. Steering flow should favor passing showers across windward areas, followed by afternoon convection mainly across the interior and western to northwestern portions of Puerto Rico. Locally heavier rainfall will ultimately depend on the track and structure of Dolly and the distribution of its associated moisture.

Moisture should gradually decrease by late Tuesday as guidance indicates low to moderate concentrations of Saharan dust reaching the region. Nevertheless, precipitable water values are forecast to remain near the upper end of climatological values or above normal through much of the remainder of the period. Lingering moisture associated with Dolly, followed by another tropical wave passing mainly south of the islands Wednesday night into Thursday, should maintain periods of passing showers across windward areas and afternoon convection over Puerto Rico under persistent east- southeast flow.

Meanwhile, seasonal to above-seasonal 925-mb temperatures are expected to persist, maintaining the potential for elevated to significant heat impacts, particularly during periods of reduced cloud cover and rainfall. Given the uncertainty surrounding Dolly, continue to monitor the latest Tropical Weather Outlook from the National Hurricane Center and subsequent forecasts from NWS San Juan for changes in its evolution and potential impacts.

AVIATION

(18Z TAFS) Issued at 157 PM AST Thu Aug 27 2026

VFR condt across most TAF sites, with brief MVFR condt in the vicinity of TJBQ and TJPS. SE winds around 6 to 16 kts gradually diminishing after 28/23Z. Tropical Storm Dolly has develop and could potentially reach the islands by Sunday.

MARINE

Issued at 157 PM AST Thu Aug 27 2026

Tropical Storm Dolly has formed and is expected to reach the local waters from late Sunday into early next week. Winds may briefly become moderate to locally fresh as the system moves across the area, with seas between 5 and 7 feet, occasionally 9 feet across the Offshore Atlantic waters. Small Craft Advisory possible. Surface high pressure across the central Atlantic will promote a moderate east to east-southeast wind flow through the weekend. Expect the first round of increasing showers and isolated thunderstorms by Saturday.

BEACH FORECAST

Issued at 157 PM AST Thu Aug 27 2026

A moderate risk of rip currents will continue along the northern and eastern exposed beaches of Puerto Rico and the U.S. Virgin Islands during the next several days. Beachgoers must exercise caution, as life-threatening rip currents are possible along the surf zone. Beachgoers are urged to remain weather alert regarding the development of Tropical Storm Dolly.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>003-005- 007-008-010>013.

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

AM...None.