textproduct: San Juan

KEY MESSAGES

Issued at 240 PM AST Thu Jul 30 2026

- Increasing moisture on Friday and another tropical wave arriving Saturday afternoon will bring a higher chance of showers and thunderstorms through Sunday, increasing the potential for localized flooding, lightning, gusty winds, and reduced visibility, which could impact outdoor activities.

- Strengthening easterly winds will continue to build seas and create hazardous marine and beach conditions through the week, resulting in choppy seas.

- Hot conditions will return on Sunday across Puerto Rico and the U.S. Virgin Islands, increasing the risk of heat-related illnesses, especially for vulnerable populations, outdoor workers, and anyone spending extended periods outside.

Short Term(This evening through Saturday)

Issued at 240 PM AST Thu Jul 30 2026

Hazy skies persisted today due to moderate concentrations of Saharan dust, mostly fair weather conditions prevailed across Puerto Rico. Around noon, scattered showers due to a streamer developed near the El Yunque area, where radar estimates indicated around 0.40 inches of rainfall. Daytime high temperatures ranged from the upper 80s to the low 90s, with heat indices reaching between 108 and 113F across north-central, western, and southern Puerto Rico. An Extreme Heat Warning remains in effect through 5 PM this afternoon. Meanwhile, easterly winds generally ranged between 15 and 20 mph, with occasional gusts of 23 to 30 mph.

For the remainder of the afternoon, isolated to scattered showers driven by daytime heating, sea breeze convergence, and local effects are expected to develop across western Puerto Rico. Activity should remain limited and localized, with no significant flooding concerns, as a dry mid-level layer and extensive high cloud cover associated with an upper-level low suppress rain development.

Moderate concentrations of Saharan dust will persist through tonight before gradually decreasing Friday morning. Although dust concentrations will be less, low concentrations will still remain present. At the same time, a wind perturbation is expected to increase low-level moisture. Based on the latest guidance, precipitable water (PWAT) values are forecast to increase from around 1.5 inches (below normal, 25th percentile) to between 1.75 and 1.80 inches (near seasonal values, around the 50th percentile). This will slightly increase the potential for and frequency of passing showers across windward areas, as well as the coverage of afternoon convection across western Puerto Rico, where isolated thunderstorms will be possible. A limited flood risk is being highlighted for northeastern and metropolitan Puerto Rico due to the potential for El Yunque streamer formation, as well as across western sectors where afternoon convection is expected on Friday.

By late Saturday morning onward, moisture associated with a tropical wave is expected to arrive, accompanied by lighter southeasterly winds. PWAT values are projected to increase to seasonal or above-normal levels, with additional moisture extending into the mid and upper levels, according to the latest GFS cross-section analysis. The 500-mb temperature is forecast to cool to around -7C, increasing the potential for thunderstorm development. However, the development and intensity of rainfall will also depend on how much upper-level cloud cover develops. Continue to monitor the forecast as updates become available and forecast uncertainty decreases.

For the remainder of the short-term forecast period, a limited or elevated heat risk will likely persist. Residents and visitors are encouraged to stay hydrated and continue practicing heat safety measures.

Long Term(Sunday through Thursday)

Issued at 340 AM AST Thu Jul 30 2026

Variable conditions should continue in the long-term forecast, with the best chance of precipitation early next week. As mentioned in previous discussions, a broad surface high pressure lingering over the central Atlantic should mainly maintain an ESE-SE wind flow, with locally breezy conditions. The latest global model solutions suggest lingering moisture associated with a tropical wave and an upper-level low located over Hispaniola. Based on the deterministic guidance of the GFS and ECMWF, PWAT values should remain between 1.8 and 2.0 inches, with localized areas reaching 2.2 inches, slightly above climatological normal.

Looking at the cross-section, low-level moisture content should remain seasonal to above-normal (60-80%), while mid-level moisture content may reach two standard deviations above normal (up to 80%). In terms of instability, the proximity of the upper-level low should maintain cool mid-level temperatures (500 mb temperatures around -6 and -7 degrees Celsius), with the best vorticity and divergence east of the CWA, which should allow cloud growth and deeper convection. Additionally, the Galvez-Davison Index (GDI) suggests the potential of isolated to scattered thunderstorms moving across the local islands during Sunday morning. These conditions may lead to an advective pattern during the morning hours, with afternoon convection over portions of western/northwestern Puerto Rico, including local islands streamers. Rainfall accumulations could result in ponding of water over roadways and poorly drained areas, including localized urban and small stream flooding.

As the upper-level low migrates northwest, the latest guidance suggests a drier air mass filtering into the region, with low- to mid-level RH plummeting to below climatological values (between 20 and 40%). Additionally, the NASA GEOS Dust Extinction suggests a dense plume of Saharan dust moving across the region on Monday morning, likely to bring hazy skies, reduced visibility, and deteriorating air quality. Although the combination of daytime heating, local effects, and available moisture may lead to afternoon convection over western Puerto Rico, shower activity may become short-lived with low rainfall accumulations. A similar pattern is likely on Tuesday, while shower activity should increase once again on Wednesday, as a trough approaches the CWA.

Under an ESE-SE wind flow, warmer to hotter temperatures can be expected across the CWA, particularly over urban and low-lying areas. With periods of high moisture content and the influence of Saharan dust, maximum temperatures should remain in the low 90s, while heat indices will likely exceed 100 degrees Fahrenheit. Therefore, the heat threat will remain elevated throughout the forecast period.

AVIATION

(18Z TAFS) Issued at 240 PM AST Thu Jul 30 2026

Mainly VFR conditions are expected during this forecast period. TJBQ may observe -RA/VCSH thru 30/20-21Z. The presence of low to moderate concentrations of Saharan dust will maintain slight reductions in visibility and hazy skies. from this afternoon into the coming days. Another aviation concern will be the winds, with gusts near 30 kts expected today thru 30/23Z, then around 10 kts overnight. Winds increasing again after 31/13-14Z.

MARINE

Issued at 240 PM AST Thu Jul 30 2026

The surface high pressure over the central Atlantic will continue to build and strengthen through early next week. This will promote moderate to fresh trades for the next few days. These conditions will maintain choppy seas across the regional waters and passages through at least Saturday. Moderate concentrations of Saharan dust will continue to cause hazy skies and slightly reduced visibilities through early Friday.

BEACH FORECAST

Issued at 240 PM AST Thu Jul 30 2026

Breezy conditions will support a moderate risk of rip currents across most of the east, north, and southern beaches of Puerto Rico, and the U.S. Virgin Islands through Saturday. The risk is expected to drop along the southern beaches of Puerto Rico, Vieques, Culebra, and the USVI by Sunday. Nevertheless, beachgoers should be aware that life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. Hazy conditions will continue through tonight across all the islands due to Saharan dust.

FIRE WEATHER

Issued at 240 PM AST Thu Jul 30 2026

Based on surface observations, minimum relative humidity values have been near or above critical thresholds today. Similar conditions are expected tomorrow. Critically dry fuels persist across southern Puerto Rico and St. Croix, with Keetch-Byram Drought Index (KBDI) values remaining well above the critical threshold. East winds are expected to remain above or near the critical levels through at least tomorrow, slightly which could promote the rapid spread of any fire that develops.

SJU WATCHES/WARNINGS/ADVISORIES

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

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

AM...None.