textproduct: San Juan

KEY MESSAGES

Issued at 214 PM AST Sun Aug 9 2026

- A Heat Advisory remains in effect through 5 PM for the lower elevations of Puerto Rico and the U.S. Virgin Islands.

- A drier air mass and suspended Saharan dust will build across the local region through Monday, suppressing widespread convective activity and leading to hazy skies and elevated heat indices through early Tuesday.

- Moisture returns rapidly late Tuesday ahead of an approaching tropical wave, increasing shower and thunderstorm coverage and restoring localized flooding risk.

Short Term(This evening through Tuesday)

Issued at 214 PM AST Sun Aug 9 2026

A weak tropical wave and a dense Saharan Air Layer generated a combination of showery and hazy conditions across the islands early today. The Doppler radar estimated up to 2 inches of rain in Rio Grande and less than half an inch across the eastern interior. After the quick surge in morning showers, drier and hot conditions prevailed in general through early this afternoon, with heat indices ranging between 104F-112F across most coastal and urban areas of the lower elevations of PR and the USVI. For the rest of this afternoon, breezy and hazy conditions will prevail, with locally induced showers developing mainly over the west coast of PR.

Similar conditions will continue on Monday as a patch of dry, Saharan dust-laden air lingers over the northeastern Caribbean. Layered precipitable water observations and regional aerosol guidance indicate precipitable water dropping sharply toward the 25th percentile (near 1.50 inches), while mid-level relative humidity falls below 30 percent. Strong mid-level subsidence will cap deep convection across most of PR and the USVI through Monday night into early Tuesday. Under hazy skies, daytime heating and surface humidity will push heat indices once again around 108F along coastal and urban areas, warranting another heat advisory issuance.

By Tuesday, the dust mass shifts westward as the leading edge of a tropical wave arrives from the east. Deep-layer moisture will rapidly increase, pushing precipitable water back above 1.80 inches. High-resolution guidance and atmospheric soundings indicate rising 850700 mb relative humidity alongside falling 500 mb temperatures, destabilizing the atmosphere. As a result, coverage of scattered showers and thunderstorms is expected to increase in general across the islands, shifting the primary hazard back toward urban flooding and localized river rises heading into mid-week.

Long Term(Wednesday through next Saturday)

Issued at 214 PM AST Sun Aug 9 2026

Weather conditions during the long-term period will start off variable as a tropical wave moves over the islands and wind speeds continue to gradually increase. Precipitable water (PWAT) values will start off at generally normal values (up to around 2 inches) as the wave moves over the islands. The interaction between this wave and the atlantic surface high will result in a breezy to locally windy, E to ESE, steering flow. Along with diurnal heating, sea breeze convergence and local effects, this setup will help trigger afternoon convection across interior to W-NW PR, as well as lines of showers downwind of El Yunque and the local islands. Passing showers will also reach windward sectors. The heaviest showers could promote ponding of water and sustain a flooding risk. Low to moderate concentrations of Saharan Dust will also persist to start the long term period and continue through at least the workweek. Drier air will reach the islands on Thursday, limiting widespread shower activity, with breezy to locally windy flow also limiting accumulations. Increasing uncertainty develops Friday onward as the tropical waves that would affect the region Friday and during the next weekend are currently being monitored by the National Hurricane Center (NHC). The latest 2 AM Tropical Weather Outlook has these waves with a low and medium formation chance, respectively. Although the forecast has been based on the typical weather pattern under generally increasing moisture and breezy to windy easterly flow. Due to the extended forecast window, adjustments to the track and intensity of the moisture remain possible toward the end of the period. Please continue to monitor the latest Tropical Weather Outlooks (TWOs) issued by the NHC for more information regarding the formation chance of these tropical waves.

AVIATION

(18Z TAFS) Issued at 214 PM AST Sun Aug 9 2026

Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. VCTS possible at TJBQ thru 09/23z. The 09/12z TJSJ sounding indicated ENE winds at 28 kt just blo FL020. HZ due to Saharan dust will continue through Monday, and VSBY may drop to 6SM.

MARINE

Issued at 214 PM AST Sun Aug 9 2026

A combination of a surface high pressure over the central Atlantic and a passing tropical wave continue to promote breezy conditions across the local waters, resulting in occasionally choppy seas of up to 6 feet. Therefore, small craft operators should exercise caution across the regional waters. Showers and thunderstorms associated with the tropical wave are expected to remain across the local waters, resulting in locally hazardous marine conditions. Another tropical wave will approach the region by Tuesday, increasing the potential for showers and thunderstorms over the local waters. By the end of the workweek, a strengthening surface high over the central Atlantic will promote increasing easterly winds, resulting in hazardous conditions for small craft, with winds of 15 to 20 knots, locally up to 25 knots, and seas potentially building to 5 to 7 feet.

BEACH FORECAST

Issued at 214 PM AST Sun Aug 9 2026

A moderate risk of rip currents will continue along the northern, eastern, and southeastern beaches of Puerto Rico, Culebra, Vieques and St. Croix through at least Tuesday. Breezy easterly winds associated with a surface high pressure over the central Atlantic and passing tropical waves will maintain choppy surf conditions, particularly along exposed northern and eastern beaches. A low risk will return on Wednesday across most beaches, before increasing to moderate Thursday and potentially high Friday into next weekend as easterly winds strengthen significantly in response to the high pressure system.

SJU WATCHES/WARNINGS/ADVISORIES

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

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

AM...None.