textproduct: San Juan

KEY MESSAGES

Issued at 317 AM AST Mon Aug 17 2026

- An elevated heat threat will persist throughout the workweek due to warm temperatures and heat indices exceeding 108 degrees Fahrenheit.

- A Heat Advisory is in effect from 10 AM to 5 PM AST for urban and coastal areas of Puerto Rico and the U.S. Virgin Islands.

- Dry conditions will persist through late Tuesday, with very limited shower activity during the period.

- A tropical wave will approach the local islands by Wednesday, increasing the potential for showers and thunderstorms.

Short Term(Today through Wednesday)

Issued at 317 AM AST Mon Aug 17 2026

Tranquil and generally quiet weather prevailed across the region overnight, with Doppler radar picking up fast-moving showers over Caribbean waters while land areas stayed mostly clear. Overnight lows ranged from the upper 70s to low 80s in coastal and urban areas, dropping into the 70s across higher elevations. Winds remained light out of the east at 5 to 10 mph, with land breeze variations and occasional higher gusts.

An elevated heat risk will affect coastal and urban sections of Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands today, where a Heat Advisory remains in effect from 10:00 AM to 5:00 PM AST. These conditions significantly increase the risk of heat exhaustion and heat stroke, especially for young children, the elderly, and anyone spending extended time outdoors. Stay hydrated, limit direct sun exposure, and take frequent breaks in the shade or air conditioning.

Dry, stable air aloft will keep precipitable water (PWAT) values below normal, between 1.25 and 1.45 inches through Tuesday, limiting rain chances. Nonetheless, daytime heating and local effects could trigger isolated showers over western Puerto Rico during the afternoon. A tropical wave will approach the region from late Tuesday evening into Wednesday, pulling in deep moisture and driving PWAT values above-normal values of 2.00 inches. This shift will sharply increase the potential for widespread showers and thunderstorms across Puerto Rico and the U.S. Virgin Islands. Given the ongoing dry spell, any rain will be a welcome relief. Please continue to monitor the forecast closely throughout the week for updates as conditions evolve.

Long Term(Thursday through Monday)

Issued at 317 AM AST Mon Aug 17 2026

A generally quiet weather pattern is expected through most of the period, with no significant rainfall hazards anticipated. Moisture should gradually decrease Thursday into Friday, favoring brief passing showers and limited afternoon convection over western Puerto Rico. Heat will likely remain the main concern, with elevated heat risk possible where sufficient sunshine occurs.

Forecast confidence decreases toward the end of the period as some guidance suggests an open tropical wave approaching the northeastern Caribbean by Sunday or the following weekend. At this range, however, the signal remains highly uncertain and may partly reflect climatological influences in the model solutions rather than a well- defined system. Trends will continue to be monitored.

AVIATION

(06Z TAFS) Issued at 317 AM AST Mon Aug 17 2026

Mainly VFR conds expected across all TAF sites. Today, generally fair weather conditions will prevail across the region with aftn SHRA across western PR. Light winds btw 5-10 kts through 17/13-14Z. Breezy conditions with occasional gusts up to 26 kt will persist through 17/23Z. VCSH possible overnight across USVI sites and TJSJ, but overall no significant impacts expected.

MARINE

Issued at 317 AM AST Mon Aug 17 2026

Moderate trade winds will prevail over the region for the next few days. Expect hazy skies from Saharan dust across the northeastern Caribbean, with a weak tropical wave bringing increased showers and possible thunderstorms with gusty winds by midweek. Choppy 6-foot seas will ease to 3-4 feet later in the workweek.

BEACH FORECAST

Issued at 317 AM AST Mon Aug 17 2026

Winds and seas are expected to gradually improve today across the coastal waters of the islands, and a moderate risk of rip currents is expected to prevail across the north and east facing beaches of the islands. A low to moderate risk of rip currents is expected through most of the workweek as seas subside through midweek. However, remember that even when the risk is low, life-threatening rip currents can occur near groins, jetties, reefs, and piers. Shower and thunderstorm activity could increase on Wednesday with the arrival of the next tropical wave.

FIRE WEATHER

Issued at 317 AM AST Mon Aug 17 2026

Critical fuel conditions persist across the islands, with extreme drought affecting portions of eastern Puerto Rico and the southern coastal plains. A drier airmass continues to promote mostly fair weather across the region while lowering relative humidity to critical levels. Combined with ongoing rainfall deficits, stressed vegetation, and dry fuels, these conditions will favor rapid fire spread.

The greatest concern remains across southern and southwestern Puerto Rico, where fuels are exceptionally dry and recent fire activity has been frequent. However, elevated fire danger extends across all of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands. Consequently, a Fire Danger Statement is in effect from 10:00 AM to 500 PM AST. Residents and visitors are strongly urged to avoid outdoor burning, as conditions will easily support wildfire ignition and rapid spread.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ001-002.

AM...None.