textproduct: San Juan

KEY MESSAGES

Issued at 345 AM AST Sun Aug 2 2026

- Influx of tropical moisture from a surface trough east of the Anegada Passage, and lingering instability, will increase the chance of showers and t-storms today, which may result in localized flooding and disruptions to outdoor activities.

- Moderate to high concentrations of Saharan Dust are forecast to arrive late tonight through Tuesday, resulting in deteriorated air quality and hazy skies.

- 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.

- Up to a moderate risk of rip currents will persist through Monday, and possibly returning by Thursday.

Short Term(Today through Tuesday)

Issued at 345 AM AST Sun Aug 2 2026

Current satellite-derived Precipitable Water (PWAT) imagery evidence both high end normal to above normal (above 2 inches) of PWAT over the area and a continuous influx of similar levels of moisture from the south-southeast. Under an east-southeast flow, showers and isolated t-storms are also being steered from mainly the southern waters. Since midnight, the highest, radar-estimated, rainfall accumulations have remained over the waters while, generally minimal accumulations were detected over the eastern third of Puerto Rico as well as over southern PR. According to official and unofficial stations, lows ranged from the mid-to- upper 70s and low 80s, across urban and lower-elevation areas of the islands, to the 60s across higher elevations of Puerto Rico.

Although the axis of yesterdays tropical wave is west and away from the islands, lingering moisture from this system as well additional moisture from a surface-induced trough over the Lesser Antilles will continue to be steered over the region today. This will continue to result in high end normal to above normal PWAT values over the region through tonight. Lingering instability due to an upper-level trough west of the region as well as seasonal 500 mb temperatures through the period, will aid in t-storm development. Morning hours will see passing showers across windward areas, with afternoon t- storms subsequently forming over the interior and tracking toward W- NW Puerto Rico, and possibly downwind of El Yunque and the local islands. These t-storms, particularly over interior to W-NW PR, will develop due to available moisture, lingering instability, diurnal/local effects and sea-breeze convergence; these can result in localized higher rainfall amounts, sustaining a flooding risk, lightning risk and isolated stronger wind gusts.

An influx of moderate to high concentrations of Saharan Dust is anticipated to bring a drier weather pattern late tonight through Tuesday as the upper level trough west of the region also weakens. PWAT values are forecast to sharply decrease to become below normal to normal (1.5 to 1.75 inches) with locally higher values during afternoon convection and with patches of moisture moving over the region. Monday is forecast to be the driest day of the period, as patches of moisture become more frequent on Tuesday. These moderate to high concentrations of Saharan Dust will result in hazy skies, lower visibilities, and deteriorated air quality Monday and Tuesday. Sensitive groups should follow the Health Department recommendations, keep their medications handy and avoid outside activities. Diurnal heating, local effects and sea breeze convergence will still result in afternoon convection (showers and possible isolated t-storms) mainly over interior to west-northwest PR on Monday under east-southeasterly flow and over interior to west- southwest PR on Tuesday as winds back to become more east- northeasterly. Showers will also be steered towards windward areas, likely more frequently on Tuesday. Current guidance suggests that Saharan Dust concentrations will gradually decrease on Tuesday, leaving low concentrations Tuesday night and into the long term period.

Breezy conditions continue to be possible at coastal areas during the period. Heat risks will also persist to start the week as 925 mb temperatures will continue above normal. Heat indices are forecast to reach and surpass the low 100s during each late morning to afternoons over urban and lower elevation sectors of the islands, with some relief possible, most likely today, with the above mentioned showers. Heat Products could be issued for each late morning to late afternoon; continue to monitor the forecast for updates.

Long Term(Wednesday through Sunday)

Issued at 345 AM AST Sun Aug 2 2026

A tropical wave is expected to move across the region by Wednesday, increasing the potential for showers and isolated thunderstorms. The latest precipitable water (PWAT) analysis shows seasonal values ranging from 1.75 to 2.00 inches from Wednesday through early Thursday morning. Under this pattern, passing showers are anticipated across the U.S. Virgin Islands and eastern Puerto Rico, followed by afternoon convective activity over the interior and western Puerto Rico. This daily activity will be driven by the combination of available moisture, diurnal heating, and local terrain effects.

Following the passage of the wave, a broad high-pressure system extending across the western and central Atlantic will bring drier air and more stable conditions to the area under an east-southeast wind flow. While trade winds may occasionally drag small patches of moisture across the region, no significant rainfall is expected during this timeframe. However, excessive heat will persist due to above-normal temperatures at the 925 mb level, with daytime highs reaching the upper 80s to low 90s across coastal and urban areas each day. These temperatures, combined with the east-southeasterly winds and the available moisture, could lead to high heat indices throughout the period. Please continue to monitor weather conditions as the week progresses.

AVIATION

(06Z TAFS) Issued at 345 AM AST Sun Aug 2 2026

Mainly VFR conditions through the period. Passing SHRA, with possible isolated -TSRA, over the region under ESE flow. After 02/13Z, ESE sfc winds increase to 10-18 kts with higher gusts and sea breeze variations, before becoming light after 02/23Z. After 02/17-18Z, SHRA/-TSRA can develop over interior to western PR and downwind of the local islands and El Yunque, affecting TJBQ/TJSJ and possibly resulting in brief MVFR conditions. HZ over TIST/TISX after 03/01Z and over TJSJ/TJPS after 03/05Z.

MARINE

Issued at 345 AM AST Sun Aug 2 2026

A surface trough east of the Anegada Passage is expected to bring showers and thunderstorms across the region today. A surface high pressure over the central Atlantic will continue to promote moderate to locally fresh trades through next week. Seas and winds are expected to reach small craft advisory criteria today. Additionally, locally stronger winds due to the sea breeze are expected each afternoon across the Atlantic and Caribbean coastal waters of Puerto Rico. Hazy conditions will return on Monday due to Saharan dust.

BEACH FORECAST

Issued at 345 AM AST Sun Aug 2 2026

Wind-driven waves will continue to support a moderate risk of rip currents across the northwest to southeastern beaches of Puerto Rico, Vieques, Culebra, and St. Croix. A low risk is expected across the western to southern beaches of PR, and most beaches of St. Thomas and St. John. 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 345 AM AST Sun Aug 2 2026

Influx of moisture today 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.