textproduct: San Juan

KEY MESSAGES

Issued at 248 PM AST Sat Aug 1 2026

- Periods of showers and thunderstorms associated with afternoon convection and a passing tropical wave will continue across north-central and western Puerto Rico today, increasing the risk of localized flooding and disruptions to outdoor activities.

- Low concentrations of Saharan dust will persist through tomorrow evening before increasing to moderate to high levels by the start of the workweek, leading to hazy skies and deteriorating air quality.

- Significant to elevated heat risk will persist across lower elevations and urban areas of Puerto Rico and the U.S. Virgin Islands through most of the period, increasing the potential for heat- related illnesses, especially during the workweek.

Short Term(This evening through Monday)

Issued at 248 PM AST Sat Aug 1 2026

Variable weather conditions prevailed across the local islands this morning as deep tropical moisture associated with a departing tropical wave continued to stream across the region. Passing showers affected windward coastal areas, while streamer activity developed downwind of the U.S. Virgin Islands and north of the San Juan metro area. One of these bands produced heavy showers just north of the Luis Munoz Marin International Airport, where a waterspout was reported downwind of this area, just offshore near Balneario El Escambron. Across western Puerto Rico, skies remained partly cloudy to mostly sunny through the morning.

The 01/12Z TJSJ sounding sampled a very moist environment, with precipitable water increasing to 2.08 inches, well above normal for this time of year. Combined with lingering instability aloft associated with an upper-level trough west of the islands, conditions became favorable for afternoon convection. As expected, showers and thunderstorms developed over the interior and western sections of Puerto Rico, producing locally heavy rainfall, frequent lightning, and isolated gusty winds.

For Sunday, although the axis of the tropical wave will be well west of the region, its trailing moisture will remain in place while additional low-level moisture associated with a surface-induced trough currently east of the forecast area lifts northward across the northeastern Caribbean. Forecast soundings continue to indicate above-normal precipitable water values near or around 2 inches through much of the day, along with sufficiently moist mid-level conditions to support another active convective afternoon. Passing showers will once again affect the windward sectors during the morning, followed by thunderstorms developing over the interior and spreading toward western and northwestern Puerto Rico during the afternoon. While rainfall coverage is not expected to be widespread enough to provide meaningful drought relief, localized higher rainfall totals are possible beneath stronger thunderstorms. The combination of abundant moisture, lingering upper-level instability, and local sea-breeze convergence may also support a few stronger thunderstorms capable of producing frequent lightning, isolated wind gusts, and localized flooding, especially across western Puerto Rico.

A drier pattern is expected to develop Sunday night into Monday as a Saharan Air Layer moves into the region. Model guidance shows precipitable water values decreasing to below normal or near seasonal levels while mid-level moisture also declines. As a result, Monday should be the driest day of the period, with hazy skies, reduced air quality, and less widespread convection. Nevertheless, afternoon showers and isolated thunderstorms remain possible across the interior and western Puerto Rico due to daytime heating, sea breeze convergence, and local effects. Heat indices will continue to exceed 100 degrees across urban and lower elevations each afternoon.

Long Term(Tuesday through next Friday)

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

(18Z TAFS) Issued at 248 PM AST Sat Aug 1 2026

Mainly VFR conds will prevail, with brief MVFR in SHRA/TSRA. VCTS expected this aftn across the interior and W PR, affecting mainly TJPS/TJBQ btwn 17-22Z with brief vsby reductions, MT OBSC, and gusty/erratic winds. Isold SHRA will continue across windward terminals at times. Sfc winds ESE 10-18 kt with higher gusts and sea breeze variations, becoming lighter aft 23Z. Waterspouts remain psbl over the local waters, especially near heavier SHRA/TSRA. One waterspout was reported this morning just offshore north of the San Juan metro area.

MARINE

Issued at 248 PM AST Sat Aug 1 2026

Tonight into Sunday, expect period of showers and thunderstorms across portions of the regional waters and passages as a tropical wave continues to move across the region. 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 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 248 PM AST Sat Aug 1 2026

A moderate risk of rip currents will persist across the northwest to southeast beaches of Puerto Rico, Vieques, Culebra, and St. Croix through tonight. A low risk is expected across the western to southern beaches of PR, and most beaches of St. Thomas and St. John tonight through Tuesday. 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, the risk will become low across all coastal areas.

FIRE WEATHER

Issued at 248 PM AST Sat Aug 1 2026

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, 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.