textproduct: San Juan

KEY MESSAGES

Issued at 208 PM AST Sat Aug 8 2026

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

- Elevated fire weather conditions may persist for the next few days across southern and southwestern Puerto Rico due to critically dry fuels, low relative humidity, and breezy conditions.

- Moderate to high concentrations of Saharan Dust will persist through Monday. Sensitive groups must follow medical recommendations.

- Limited rainfall is expected for the next several days, allowing drought conditions to continue worsening across Puerto Rico and the U.S. Virgin Islands.

Short Term(This evening through Monday)

Issued at 208 PM AST Sat Aug 8 2026

A stable and overall dry/hazy air mass will remain in place through Monday across the northeastern Caribbean. The 8/12z upper air sounding indicated a significant drying trend, with precipitable water values dropping well below normal seasonal values to 1.20 inches. Dry air in the mid-levels accompanied by a persistent trade wind cap will prevent deep vertical cloud development across most of the area. While brief, isolated trade wind showers cannot be completely ruled out across the waters between the islands and localized in western Puerto Rico this afternoon, overall rainfall accumulations will remain minimal through the rest of the weekend. However, a weak tropical wave is expected to move across the Caribbean waters through Sunday, which could enhance the typical diurnal cycle of early morning passing showers across windward areas, and shallow afternoon convection over western PR.

Even though moisture is expected to increase briefly in the low levels of the atmosphere, the primary feature dominating the environment will be a dense intrusion of the Saharan Air Layer. Aerosol tracking models and satellite aerosol observations show dust concentrations peaking on Sunday and lingering through Monday evening, bringing thick haze and reduced visibility across the region. Light cloud cover combined with strong solar radiation and warm low-level temperatures will drive daytime highs into the upper 80s and lower 90s. When combined with coastal surface humidity, afternoon heat indices will reach 102F to 108F or higher along urban and coastal areas, increasing the heat threat once again for prolonged outdoor activities. In addition, the dust event will reduce air quality, making outdoor activities hazardous for sensitive groups with respiratory conditions.

Long Term(Tuesday through next Friday)

Issued at 208 PM AST Sat Aug 8 2026

Weather conditions during the long-term period will turn more variable with the arrival of a wind surge and a tropical wave across the CWA. On Tuesday, a surface high pressure anchored over the Central Atlantic will maintain easterly winds, pushing a weak wind surge in the 700 to 500 mb layer across the area. Precipitable water values are forecast by the GFS and ECMWF to range between 1.6 and 1.8 inches, which will be enough moisture to enhance afternoon convection along the western sections of the islands. From late Tuesday into Wednesday, surface winds will shift more from the southeast due to the interaction between the Atlantic surface high and the approaching tropical wave. The peak of this moisture field is forecast for Wednesday afternoon, favoring a variable weather pattern with morning to early afternoon showers along northeastern Puerto Rico, followed by deep afternoon convection along the western coast driven by local effects. Although rainfall accumulations of 1 to 2 inches are possible with the heaviest showers, this will not be enough to mitigate existing drought conditions across the island.

A rapid drying trend is forecast by Thursday as a drier air mass moves back into the region, limiting overall shower development across the area. By Friday, global model guidance suggests another tropical wave tracking across the Caribbean region. As of today, the GFS keeps the bulk of the moisture moving over the Caribbean waters south of the local area. However, given the extended time frame of the forecast, changes to the moisture track and intensity remain possible by the end of the period.

AVIATION

(18Z TAFS) Issued at 208 PM AST Sat Aug 8 2026

Mainly VFR conditions are expected to prevail across all terminals. Moderate to high concentrations of Saharan dust will promote hazy conditions across all terminals through the rest of the weekend, and VSBY could drop to 6SM. The 08/12z TJSJ sounding indicated ESE winds up to 26kt blo FL050.

MARINE

Issued at 208 PM AST Sat Aug 8 2026

A broad surface high over the Atlantic will maintain moderate to fresh easterly winds throughout the weekend into early next week. Marine conditions will become increasingly choppy, with the highest risk for hazardous conditions Sunday into Monday, particularly across the offshore waters and local passages. Afternoon isolated thunderstorms may produce locally hazardous winds and seas, while Saharan dust may reduce visibility through Monday.

BEACH FORECAST

Issued at 208 PM AST Sat Aug 8 2026

A moderate risk of rip currents will continue along the northern and eastern facing beaches of Puerto Rico, Culebra, Vieques and St. Croix into early next week. 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.

Heat will remain the primary beach hazard this weekend, while isolated afternoon thunderstorms over western Puerto Rico may produce dangerous cloud-to-water lightning. A dense Saharan Air Layer with high concentrations of dust will continue to arrive today, promoting hazy skies and reduced visibility through early next week.

FIRE WEATHER

Issued at 208 PM AST Sat Aug 8 2026

Elevated fire weather conditions continue this afternoon across southern and southwestern plains of Puerto Rico, where critically dry fuels, extreme drought conditions and low relative humidity values are supporting an increased risk for wildfire ignition and spread. Relative humidity values have fallen into the low to mid 50s across portions of the southern coastal plains with sustained east winds of 15 to 20 mph, with higher gusts. Although isolated showers and thunderstorms remain possible across the interior and western sections of Puerto Rico through late afternoon, rainfall coverage and amounts are expected to be limited and insufficient to provide meaningful relief over the southern coastal plains, where fuels remain critically dry.

The northern periphery of a tropical wave located over the Caribbean waters will bring a slight increase in moisture levels over the southern coastal plains on Sunday. However, drier conditions will persist and combined with the ongoing rainfall deficits and critically dry fuels will support an elevated to locally critical fire weather threat each day across the southern and southwestern coastal plains of Puerto Rico. Residents and visitors should continue to avoid outdoor burning and exercise caution with activities capable of producing sparks or open flames, as favorable conditions for wildfire ignition and rapid spread are expected to persist through the weekend.

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.