textproduct: San Juan

KEY MESSAGES

Issued at 247 PM AST Tue Sep 8 2026

* Elevated to significant heat conditions will continue through the rest of the workweek, with heat indices potentially reaching 108114F, particularly across coastal and urban areas.

* From Wednesday into Thursday, two tropical waves are forecast to move across the islands, increasing the potential for showers and a limited flooding threat.

* A moderate risk of rip currents is expected along the northern and eastern beaches of Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands.

* A Saharan Air Layer with Saharan dust particles are forecast to move across the region from Thursday evening through Saturday.

Short Term(This evening through Thursday)

Issued at 247 PM AST Tue Sep 8 2026

Variable conditions have prevailed across the forecast region during the morning and early afternoon hours. Passing showers developed across eastern, interior, and southwestern Puerto Rico, favored by the south-southeasterly wind flow. More persistent shower activity developed over northwestern Puerto Rico, resulting in rainfall accumulations between 1 and 2 inches near the municipalities of Las Marias and Anasco. Some light showers were also observed by Doppler radar across portions of the north- central sections and surrounding coastal waters. Daytime heating was the main concern, with some unofficial stations across the islands reporting heat indices ranging from 105 to 110 degrees Fahrenheit, particularly along coastal and urban areas. Therefore, the Heat Advisory will remain in effect until 5 PM today. We recommend exercising caution when engaging in outdoor activities and staying well hydrated throughout the day.

Passing showers and thunderstorms will continue to develop through the rest of the afternoon across portions of Puerto Rico as the south-southeasterly steering flow continues to move the available moisture across the region. Nonetheless, rainfall activity should remain limited through the evening as a drier air mass, currently located east of the U.S. Virgin Islands, coupled with mid-level stability, inhibits the potential for deeper convective development. TPW values are forecast to decrease from around 2.0 inches to 1.5 inches by this afternoon and evening, dropping further to around 1.2 inches by Wednesday. From Wednesday morning through Thursday night, a couple of tropical waves will make their way across the forecast region, bringing moisture back to near seasonal values, with TPW values around 2.0 inches. These waves may favor the development of showers and thunderstorms across the U.S. Virgin Islands and eastern Puerto Rico by Wednesday morning, followed by afternoon convection across western Puerto Rico. A similar pattern is expected on Thursday. Model guidance suggests that Wednesday's wave will also be accompanied by moderate concentrations of Saharan dust, which should limit mid-level moisture and reduce the potential for widespread shower activity. The highest rainfall activity is expected on Thursday due to a mid-level moisture intrusion associated with the passage of the second wave. By Thursday night, model guidance suggests a gradual return to drier conditions as another dry air mass accompanied by moderate concentrations of Saharan dust moves across the islands.

Long Term(Friday through next Monday)

Issued at 247 PM AST Tue Sep 8 2026

A surface high-pressure system over the central Atlantic is expected to strengthen its pressure gradient, promoting breezy to locally windy southeasterly flow through Friday before shifting easterly from Saturday onward. On Friday, lingering moisture associated with a departing tropical wave will bring passing morning showers across the islands. However, a drier air mass will quickly move over the region, dropping precipitable water values to 1.30-1.40 inches, nearly two standard deviations below normal, and bringing stable conditions to the area. Stability will also build aloft as a mid- level ridge moves in. Moderate to locally high concentrations of Saharan dust will accompany the dry air mass, bringing hazy skies, reduced visibility, and poor air quality. Residents and visitors are urged to follow medical recommendations and closely monitor weather forecasts for updates.

Over the weekend, fast-moving morning showers are expected across portions of eastern Puerto Rico and the U.S. Virgin Islands. Afternoon showers and isolated thunderstorms fueled by daytime heating and local effects will follow, though impacts will remain limited with no flooding concerns. From Sunday through Tuesday, an upper-level low moving toward the northeastern Caribbean will gradually increase instability and bring moisture back up to seasonal levels across the region.

AVIATION

(18Z TAFS) Issued at 247 PM AST Tue Sep 8 2026

Mainly VFR conditions are expected during the next 12-18 hours across the local terminals. However, a weak tropical wave will increase SHRA and iso TSRA around 09/04z across the USVI terminals and by 09/08z at TJSJ. This activity may cause tempo MVFR conds and mtn tops obscd across eastern PR. Locally induced TSRA expected to develop aft 06/16z at TJBQ. The 08/12z TJSJ sounding indicated ESE winds up to 19 kt blo FL120.

MARINE

Issued at 247 PM AST Tue Sep 8 2026

A surface high pressure strengthening across the central Atlantic will promote moderate to fresh winds, with stronger gusts for the rest of the week. This will result in choppy to locally rough marine conditions. Seas will build up to 6 feet across the offshore waters and local passages, with occasional seas up to 8 feet. Two back to back tropical waves will increase showers and thunderstorms across the regional waters from late tonight through midday Wednesday, and once again from Wednesday night through Thursday afternoon. Gusty winds, brief periods of torrential rainfall, and locally higher seas are expected with these tropical waves.

BEACH FORECAST

Issued at 247 PM AST Tue Sep 8 2026

Increasing winds and building seas across the coastal waters of the islands will promote a moderate risk of rip currents across most east, south, and north-facing beaches of the islands through the end of the week. A moderate risk means that life-threatening rip currents are possible in the surf zone, and beachgoers are urged to exercise caution.

Other beach hazards include heat, gusty winds and lightning strikes during the afternoon hours. Beachgoers should remain hydrated and limit prolonged sun exposure, and seek shelter whenever they hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

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

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

AM...None.