textproduct: San Juan

KEY MESSAGES

Issued at 105 PM AST Fri Sep 11 2026

- A deep Saharan Air Layer (SAL) continues to bring high concentrations of Saharan Dust. Tease conditions are expected to persist well into Sunday morning.

- An Extreme Heat Warning for mainland Puerto Rico and Heat Advisory for the US Virgin Islands, Culebra, and Vieques remains in effect until 5 PM today. Therefore, people should limit outdoor activities and remain hydrated.

- A low pressure system at high levels will settle to the north/northwest of the forecast region. Conditions are expected to become more favorable for the development of localized convection, especially over the interior and western regions of Puerto Rico. Flooding threat remains limited.

- Breezy conditions will prevail through the weekend, especially along coastal and exposed areas.

- Moderate rip current risk expected today along the northern, eastern and southeastern beaches of Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands.

Short Term(This evening through Sunday)

Issued at 105 PM AST Fri Sep 11 2026

Hazy skies, reduced visibility, and deteriorated air quality prevailed today as a Saharan Air Layer (SAL) continues to filter into the region bringing high concentrations of dust to the US Virgin Islands and Puerto Rico. Conditions remain thermodynamically unfavorable for the development of deep convection as a the thick SAL is leading to a strong inversion near 800 millibars. One of the main concerns for the rest of today is the Significant Heat Risk for mainland Puerto Rico and Elevated Heat Risk for the US Virgin Islands, Vieques and Culebra. With heat indices ranging between 100 to a 112 degrees Fahrenheit across the coastal and urban sectors of Puerto Rico, and 85-90 along the interior of Puerto Rico. Thus, an Extreme Heat Warning (Puerto Rico) and a Heat Advisory (US Virgin Islands, Vieques and Culebra) remains in effect until 5 PM today. Consequently, the potential for the development of showers remains limited for today.

Similar weather conditions will prevail through early Sunday, as high concentrations of Saharan Dust will persist over the region. Individuals in sensitive groups, such as those with respiratory conditions, young children, and older adults, should take appropriate precautions, limit prolonged outside activities and follow the recommendations of health officials. With limited cloud cover and enhanced SAL, heat conditions are forecasted to persist for the rest of the short term period. While the heating is expected mainly during the daytime, nighttime minimums are also expected to be higher than usual due to radiative effects caused by the Saharan Dust which will limit nighttime cooling.

Conditions are expected to shift to a more humid seasonal pattern by Sunday morning as the SAL leaves the County Warning Area(CWA) and an upper level low pressure settles into the region. This pattern will be more favorable for the development of convection, especially across the interior and western regions of Puerto Rico. Nonetheless, model guidance suggests that deep convection might remain limited and localized due to a drier mid level air intrusion and remnants of the SAL.

Long Term(Monday through next Thursday)

Issued at 328 AM AST Fri Sep 11 2026

A surface high pressure will continue to promote easterly- southeasterly breezy winds for most of the period. Variable conditions are expected from Monday morning until Tuesday morning, due to a drier slot in the mid levels, lowering PWAT values (between 1.2 and 1.4 inches, isolated areas up to 1.6 inches). Nevertheless, the proximity of an upper-level low could increase instability and enhance deeper convection in the area. Therefore, showers and thunderstorms during the afternoon hours could lead to ponding of water over roadways and poorly drained areas, including the possibility of urban and small stream flooding over western Puerto Rico. By Tuesday, moisture associated with a tropical wave is expected to approach the local area by Tuesday afternoon, enhancing shower activity once again across western portions of Puerto Rico, with a limited flooding risk. On Wednesday, as the upper-level low departs the region and a mid-to- upper level ridge approaches the eastern Caribbean, lingering moisture will still bring passing showers across windward sections of the islands during the morning, with afternoon convection across interior and northwestern Puerto Rico. By Thursday, another tropical wave is forecasted to reach the islands, as the latest model guidance suggest an increase in moisture content (PWAT values between 1.9 and 2.1 inches). Nevertheless, there's uncertainty regarding the time of arrival of this feature, as the latest ECMWF suggest the arrival by early Thursday, while the GFS suggests it could reach the area a bit later (Thursday afternoon and evening). Therefore, expect shower and thunderstorm activity, though the flooding threat could vary depending on the timing of the tropical wave.

Under a easterly-southeasterly wind flow, warmer conditions can be expected throughout the long-term period, particularly by the beginning of the next workweek. With abundant tropical moisture, heat indices are very likely to exceed 100 degrees Fahrenheit, increasing the heat risk. Therefore, a limited to elevated heat threat is expected across the islands, and heat products may be issued if required; please continue to monitor the forecast for any updates.

AVIATION

(18Z TAFS) Issued at 105 PM AST Fri Sep 11 2026

VFR conds will prevail. Saharan dust will maintain HZ and VSBY around 6SM at all terminals through the period. E-ESE winds 15-20 kt with gusts 23-28 kt will continue through this aftn, strongest at TJPS/TJBQ. Winds will diminish after 22-23Z, then increase again after 12/15Z with gusts 23-27 kt.

MARINE

Issued at 105 PM AST Fri Sep 11 2026

The pressure gradient between a strengthening ridge north of the region and the Colombian low will maintain moderate to fresh easterly winds tonight and through the weekend, with the strongest winds across the Caribbean waters and passages. These winds will result in choppy seas of 4 to 5 feet, occasionally up to 6 feet. Small craft should exercise caution. Saharan dust will continue through Saturday night, limiting shower activity and reducing visibility. Moisture will increase late in the weekend into early next week, favoring an increase in shower activity.

BEACH FORECAST

Issued at 105 PM AST Fri Sep 11 2026

A moderate risk of rip currents will continue along the northern, eastern, and southeastern beaches of Puerto Rico, as well as Culebra, Vieques, and the U.S. Virgin Islands through the weekend. Life-threatening rip currents remain possible in these areas, while a low risk is expected along western and more protected beaches. However, dangerous rip currents can still occur near groins, jetties, reefs, and piers.

Saharan dust will continue to promote hazy skies and reduced visibility through at least Saturday night. An increase in shower and thunderstorm activity is expected late Sunday into early next week, particularly across western Puerto Rico. Beachgoers should remain alert for lightning and rapidly changing weather conditions, and seek shelter if thunderstorms approach.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Extreme Heat Warning until 5 PM AST this afternoon for PRZ001>011.

Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.