textproduct: San Juan

KEY MESSAGES

Issued at 328 AM AST Fri Sep 11 2026

- Dense Saharan dust will remain the dominant feature today and Saturday, with high to locally very high concentrations. This will result in hazy skies, reduced visibility, and deteriorated air quality.

- Warm to hot conditions will continue, with an elevated to significant heat risk most days. Today, from 10 AM to 5 PM, an Excessive Heat Warning will be in effect for Puerto Rico, and a Heat Advisory will be in effect for the USVI, Vieques and Culebra.

- Increasing shower and thunderstorm activity is expected Sunday, especially across western Puerto Rico.

- 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(Today through Sunday)

Issued at 328 AM AST Fri Sep 11 2026

alm conditions were experienced over the islands as a dense Saharan Air Layer (SAL) continued to filter in. Lows were in the upper 70s to low 80s across urban and lower elevation areas of Puerto Rico, in the low 80s across Vieques, Culebra and the USVI, and in the 60s to low 70s across higher elevations of Puerto Rico.

The dense SAL will be the dominant feature today as it continues to move over the islands. High concentrations, locally very high at times, of Saharan Dust will continue to spread over the islands today and tomorrow, Saturday. These high concentrations of Saharan Dust will result in hazy skies, reduced visibility, and deteriorated air quality. Individuals in sensitive groups, such as those with respiratory conditions, young children, and older adults, should take appropriate precautions, follow health officials' recommendations, and limit prolonged outdoor exposure. Saharan dust concentrations are forecast to gradually decrease late Saturday night into the overnight hours on Sunday as the SAL moves westward and out of the region. Current guidance suggests that moderate concentrations should move out of the region by early Sunday morning with low concentrations thereafter.

Warm to hot conditions (particularly each late morning to afternoon) are expected at least through the rest of the week as the drier and hazier pattern continues; an elevated to significant heat risk will be present over the islands. From 10 AM to 5 PM AST, today, an Excessive Heat Warning will be in effect for Puerto Rico (particularly across coastal and urban areas and lower-elevation valleys) and a Heat Advisory will be in effect for St. Thomas, St. John, St. Croix, Vieques and Culebra. Follow health officials' recommendations, stay hydrated, stay in an air-conditioned room if possible and stay in the shade. Overnight heat trapping by the Saharan Dust will also result in warmer lows tonight and Saturday night.

Breezy conditions will prevail through the weekend especially along coastal and exposed areas, due to a surface high pressure north of the islands. The steering flow, however, will vary throughout the short term period: today will start with an ESE flow but will gradually back as the day continues becoming E by Saturday and ENE by Saturday afternoon. Steering flow is then forecast to veer and become more E by Sunday and ESE once again by Sunday afternoon. These winds can steer brief passing showers over windward sectors. Diurnal heating, sea breeze convergence, local orographic effects and available moisture can also result in showers over portions of interior and western Puerto Rico each afternoon. However, the SAL will serve to suppress deep convection today and Saturday. An upper-level trough, however, will start to approach the islands later today and persist mainly north and northwest of the islands through the rest of the short term period. This feature may slightly increase the potential for showers. By Sunday however, with Saharan dust concentrations decreasing to low, available moisture increasing, the upper trough still near the region and a weak tropical wave is moving mainly south of the islands, the potential for showers and t-storms further increases especially during afternoon convection. 500 mb temperatures are forecast to cool to around -8 C and precipitable water (PWAT) is forecast to increase to more seasonal values. Due to this, at least a limited flooding risk over sectors of western Puerto Rico is forecast during the afternoon hours.

Long Term(Monday through Friday)

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

(06Z TAFS) Issued at 328 AM AST Fri Sep 11 2026

Mainly VFR conditions. High concentrations of Saharan dust will result in HZ and VIS at generally 6SM, with brief reductions to 5SM possible. -SHRA possible over TJBQ btwn 11/17-20z. Winds up to around 5 kts, through 11/13z, then ESE at up to around 15 to 20 kt, with sea breeze variations and stronger gusts.

MARINE

Issued at 328 AM AST Fri Sep 11 2026

A strengthening surface high pressure across the central Atlantic will continue to promote moderate to fresh winds today and through the weekend. These winds will maintain choppy marine conditions, with seas generally around 4 to 5 feet, occasionally reaching 6 feet across most local waters and Caribbean passages. High concentrations of Saharan dust particles will likely remain across the region today through at least Saturday night, resulting in hazy skies and reduced visibility. Isolated showers may move across the waters at times, but the drier airmass will generally limit widespread shower development through Saturday, with rain chances increasing by the end of the weekend into early next week.

BEACH FORECAST

Issued at 328 AM AST Fri Sep 11 2026

Today, a moderate risk of rip currents persists along the northern, eastern, and southeastern beaches of Puerto Rico, as well as in Culebra, Vieques, and the U.S. Virgin Islands. A moderate risk means that life-threatening rip currents are possible, and beachgoers are urged to exercise caution. A low risk is present across the western and more protected beaches of Puerto Rico. However, life-threatening rip currents can still occur when the risk is low, particularly near groins, jetties, reefs, and piers. Similar conditions are expected to prevail through at least Sunday. Afterward, the risk will slightly decrease in area, but the moderate risk will likely persist along exposed northern beaches.

From today through at least late Saturday, high concentrations of Saharan dust particles will be present across the region, resulting in hazy skies, reduced visibility, and poor air quality for outdoor activities. Heat will also remain an additional concern over the coming days. Beachgoers should stay hydrated and limit prolonged sun exposure.

FIRE WEATHER

Issued at 328 AM AST Fri Sep 11 2026

Despite recent wetting rains in southern Puerto Rico, elevated KBDI values demonstrate that deeper soil and fuel layers remain dry. The combination of breezy ESE winds and incoming drier air will maintain a low-to-moderate fire danger risk across these areas today, though localized spikes in threat levels remain possible. We will closely monitor evolving weather patterns and fuel moisture trends for any potential escalation in fire risk.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Extreme Heat Warning from 10 AM this morning to 5 PM AST this afternoon for PRZ001>011.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ012-013.

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

AM...None.