textproduct: San Juan

KEY MESSAGES

Issued at 1202 PM AST Wed Aug 12 2026

- Showers and thunderstorms will continue across the region as lingering moisture from a previous tropical wave moves across the islands.

- Saharan dust particles will return by Thursday, with a much drier air mass dominating the region.

- The heat threat will remain in place for the rest of the week, with hot temperatures and heat indices that could increase to around 108F, and up to 112F in isolated areas.

- Deteriorating marine and coastal conditions are forecast from Friday into the weekend. For more detailed information, read the Marine and Beach sections.

- Forecast uncertainty increases late this weekend into early next week as AL92 could approach the northeastern Caribbean, bringing increasing rain and thunderstorm potential. It remains too early to determine what impacts, if any, may occur.

Short Term(This afternoon through Friday)

Issued at 1202 PM AST Wed Aug 12 2026

Abundant tropical moisture currently lingers over the region, driving precipitable water values above 2.00 inches, well above climatological normals. Atmospheric soundings indicate strong convective instability paired with light-to-moderate low-level steering flow. Daytime heating combined with local sea breeze convergence and terrain interaction will trigger strong shower and thunderstorm development this afternoon, particularly across the interior, northern, and western portions of Puerto Rico, while scattered passing showers impact the U.S. Virgin Islands and eastern sections of PR. Strong gusty winds and urban and small stream flooding remain the main weather hazard through late this evening.

Quick drying will take place rapidly overnight into Thursday as a robust Saharan Air Layer (SAL) with moderate concentrations of dust spreads across the northeastern Caribbean. Latest model guidance shows precipitable water values collapsing to between 1.10 and 1.40 inches, nearly two standard deviations below seasonal levels, while mid-level relative humidity drops below 20 percent. This stable, dusty air mass will cap deep atmospheric convection through Friday. Consequently, shower activity will be suppressed across all the islands, limited only to shallow, brief trade wind showers across windward areas during the overnight and early morning hours, with a low probability of afternoon thunderstorms or heavy showers as on previous days over western PR. Hazy skies and poor air quality will prevail, posing potential respiratory impacts for sensitive populations.

In addition to the SAL, strengthening of the Azores High will promote a wind surge across the northeastern Caribbean by the end of the workweek. Breezy trade winds averaging 15 to 25 mph with stronger gusts are expected across the islands. These winds will also promote elevated surf action and dangerous rip currents for swimmers along the northern, eastern, and southern beaches of all the islands. Furthermore, intense solar radiation combined with the dry, dusty air layer on Thursday and Friday will push maximum temperatures into the upper 80s and low 90s. When combined with residual low-level moisture, peak afternoon heat indices will likely reach heat advisory thresholds along coastal and urban areas.

Long Term(Saturday through next Wednesday)

Issued at 205 AM AST Wed Aug 12 2026

No major changes to the long-term forecast or the uncertainty regarding AL92. Breezy to locally windy east to east-northeast winds will continue into the weekend, with gusts potentially affecting unsecured outdoor items across exposed coastal and higher-elevation areas. Winds could approach advisory levels at times. A relatively dry air mass and lower concentrations of Saharan dust will also persist, with only brief passing showers expected. Heat and fire weather concerns may continue under the dry and breezy pattern.

Forecast uncertainty increases considerably late this weekend into early next week as AL92 moves westward to west-northwestward across the tropical Atlantic. A wetter pattern with increasing showers and thunderstorms, along with greater lightning and flooding risks, is possible. However, considerable uncertainty remains regarding the system's track, intensity, timing, and any direct or indirect impacts to Puerto Rico and the U.S. Virgin Islands. Continue to monitor NHC and local forecasts.

AVIATION

(18Z TAFS) Issued at 1202 PM AST Wed Aug 12 2026

Locally induced SHRA/TSRA will continue to increase across the local terminals through at least early this evening. Tempo MVFR to brief IFR conds are possible at TJSJ/TJBQ fm 12/17-23. Across the USVI terminals brief MVFR cigs possible at times. Mtn top obscd across eastern PR. Also, HZ may reduce VIS to around 6SM at times. The 12/12z TJSJ sounding indicated ESE winds up to 16 kt blo FL050.

MARINE

Issued at 1202 PM AST Wed Aug 12 2026

A broad surface high pressure and the influence of the previous tropical wave will continue to result in moderate southeasterly winds across the region for the rest of the day. Under this pattern, the moisture field associated with the tropical wave will promote thunderstorm activity that could trigger localized hazardous marine conditions, with gusty winds and frequent lightning. As the surface high pressure develops over the central Atlantic, a tightening pressure gradient will enhance moderate to locally fresh easterly winds across the region. This will result in choppy to hazardous seas, building up to 7 feet across the exposed waters and 5 to 6 feet across the coastal waters. Given the expected conditions, Small Craft Advisories may be in effect from Thursday night through the weekend.

BEACH FORECAST

Issued at 1202 PM AST Wed Aug 12 2026

A moderate risk of rip currents will continue through Thursday for all northern and eastern exposed beaches of Puerto Rico, while southern and western coastal areas will maintain a generally low risk. Visitors and residents should remain alert this afternoon into the evening, as developing coastal thunderstorms may introduce localized hazards; immediate shelter should be taken if lightning or heavy rain occurs near the shore. Looking ahead from Friday through Monday, building trade winds will bring breezy conditions and deteriorating surf across local waters, pushing the rip current risk to HIGH for exposed coastlines. Formal High Rip Current Statements will likely be issued tomorrow, and all beachgoers are strongly urged to exercise extreme caution, swim near lifeguards, and avoid entering hazardous surf conditions over the coming days.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007- 008-010-011.

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