textproduct: San Juan

KEY MESSAGES

Issued at 322 AM AST Sat Aug 1 2026

- A tropical wave will continue to move across the region today, increasing the chance of showers and thunderstorms throughout the weekend, which may result in localized flooding and disruptions to outdoor activities.

- Choppy seas up to 6 feet will persist through today while up to a moderate risk of rip currents persist through at least Monday.

- Low concentrations of Saharan dust will continue through tomorrow evening before increasing to moderate (and possibly high) to start the workweek, this will result in deteriorated air quality and hazy skies

- Heat risks will also persist for lower elevation and urban areas of Puerto Rico and the U.S. Virgin Islands through most of the period with significant to elevated levels possible during the workweek.

Short Term(Today through Monday)

Issued at 322 AM AST Sat Aug 1 2026

Recent satellite observations show Precipitable Water (PWAT) values between 1.5 and 1.7 inches over the islands, with higher amounts of 1.8 to about 2 inches concentrated to the southern waters. Guided by an east-southeast flow, the moisture field from a tropical wave passing south of the islands, combined with an upper-level low situated west-southwest of Puerto Rico, has generated an increase in overnight showers and isolated t-storms across the region. Rainfall accumulations recorded since midnight have affected mainly St. Thomas, St. John, and the eastern third of Puerto Rico, including Vieques and Culebra. Stations show around a quarter of an inch of rain in Culebra, while isolated areas in Puerto Rico received between a quarter and slightly over half an inch. Meanwhile, stations report that overnight low temperatures ranged from the mid- to- upper 70s and low 80s across urban and lower-elevation areas of the islands, dropping into the 60s across higher elevations of Puerto Rico.

The moisture field from the above mentioned tropical wave will continue to move northward and filter over the region this morning onwards, increasing rain chances. As this influx of moisture from a tropical wave moves over the islands under an east-southeast flow, high-end normal (1.9 inches) to above-normal (2.0 inches) PWAT values will reach the region. Available moisture will extend into the mid-levels of the atmosphere. Concurrently, 500 mb temperatures are expected to drop to more seasonal levels over the weekend, creating conditions favorable for t-storm development. Showers will continue to be steered towards windward sectors during the period. A limited to elevated flooding risk remains forecast for the region, particularly during afternoon convective showers and t-storms. The areas most susceptible to these impacts include the interior and west-northwestern sections of Puerto Rico, along with potentially downwind of El Yunque and the local islands. Similar conditions are forecast tomorrow, albeit with the upper level low now west of Puerto Rico and the wave axis moving away from the region. However, above-normal moisture continues to filter over the islands under east-southeast flow as a surface high over the Atlantic persists. A limited to elevated flooding threat will persist over interior and west-northwestern Puerto Rico, and possibly downwind of El Yunque and the local islands.

Today through tomorrow evening, the islands will see a continuous influx of low Saharan Dust concentrations. A Saharan Air Layer (SAL) is then projected to arrive from the east tomorrow night, elevating Saharan Dust to moderate, or potentially high, concentrations. Expected to last through Monday and into the long-term period, these higher concentrations will cause hazy skies, lower visibilities, and deteriorated air quality. This drier air will result in below normal to normal PWAT values overnight Sunday into Monday while the upper low moves westward and away from the islands. This would leave Monday as the driest day of the short term forecast, nevertheless diurnal heating, local effects and sea breeze convergence will result in afternoon convection over interior to west-northwest PR as east-southeasterly steering flow persists. Breezy conditions are also possible at coastal areas during the period. With increasing moisture and east-southeasterly flow, heat risks will persist during the short term forecast period, with heat indices reaching and surpassing the low 100s during the late mornings to afternoons over urban and lower elevation sectors of the islands, with some relief possible with the above mentioned showers. Heat Advisories could be issued for each late morning to late afternoon; continue to monitor the forecast for updates.

Long Term(Tuesday through Saturday)

Issued at 322 AM AST Sat Aug 1 2026

Excessive heat will remain the primary hazard, with significant heat risk levels possible throughout the long-term period. Saharan dust should also linger into midweek, maintaining hazy skies and reduced air quality.

A tropical wave is expected to move across the region early to midweek, increasing shower and isolated thunderstorm activity, with the greatest potential currently anticipated on Wednesday. Despite generally drier conditions during the remainder of the period, diurnal heating and local effects should support afternoon convection each day. Widespread flooding is not anticipated at this time, although locally heavy rainfall could result in ponding of water on roads and in poorly drained areas. Forecast confidence decreases toward the end of the period.

AVIATION

(06Z TAFS) Issued at 322 AM AST Sat Aug 1 2026

Mainly VFR conditions through the period. A tropical wave will continue to result in passing SHRA over the region, with a chance of -TSRA. After 01/13-14Z, E-ESE winds increase to 10 to 18 kts with higher gusts and sea breeze variations, before becoming light with land breezes after 01/23Z. After 01/17Z, SHRA/-TSRA can develop over interior to western PR and downwind of the local islands and El Yunque, affecting TJBQ/TJSJ. This can result in brief MVFR conditions.

MARINE

Issued at 322 AM AST Sat Aug 1 2026

A tropical wave moving across the Caribbean Sea will continue to bring showers and thunderstorms across portions of the regional waters and passages today. Meanwhile, a surface high pressure extending from the central Atlantic will continue to promote moderate to locally fresh trades through next week. Occasional seas up to 6 feet are expected today across the offshore Atlantic and Caribbean waters, and the Anegada and Mona Passages. Seas and winds are expected to remain below small craft advisory criteria through next week. However, locally stronger winds due to the sea breeze are expected each afternoon across the Atlantic and Caribbean coastal waters of Puerto Rico.

BEACH FORECAST

Issued at 322 AM AST Sat Aug 1 2026

Wind-driven waves will support a moderate risk of rip currents across the northwest to southeastern beaches of Puerto Rico, Vieques, Culebra, and St. Croix today. A low risk is expected across the western to southern beaches of PR, and most beaches of St. Thomas and St. John through the weekend. Nevertheless, beachgoers should be aware that life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers even when the risk is low. By Tuesday and Wednesday, the risk will become low across all beaches of the islands.

FIRE WEATHER

Issued at 322 AM AST Sat Aug 1 2026

Minimum relative humidity values should remain near or above critical thresholds today. Influx of moisture during the weekend could aid in improving overall fire weather conditions. However, 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 to east-southeast winds are expected to remain above or near the threshold values today, slightly which could promote the rapid spread of any fire that develops. Residents and visitors should avoid outdoor burning and exercise caution with activities that could generate sparks or open flames, especially across areas with critically dry vegetation.

SJU WATCHES/WARNINGS/ADVISORIES

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