textproduct: San Juan

KEY MESSAGES

Issued at 235 AM AST Sat Jun 20 2026

* A Heat Advisory remains in effect today for coastal and urban areas of Puerto Rico and the U.S. Virgin Islands. Sensitive individuals may experience heat-related illnesses without adequate hydration, cooling, and frequent breaks from the heat.

* Moderate to high concentrations of Saharan dust will continue through at least late tonight, reducing air quality and visibility while increasing the risk of respiratory issues for sensitive groups. Dust concentrations may briefly decrease on Sunday as a tropical wave moves through the region, but are expected to increase again behind the wave and persist into early next week.

* A tropical wave moving through the region on Sunday will increase the potential for heavy rainfall, thunderstorms, urban and small-stream flooding, and isolated flash flooding across portions of Puerto Rico and the U.S. Virgin Islands.

* Dangerous heat index values will continue each afternoon through much of the forecast period, increasing the risk of heat exhaustion and heat stroke, especially in coastal and urban areas, poorly ventilated locations, and among vulnerable populations.

* Life-threatening rip currents remain possible at some exposed beaches across Puerto Rico and the U.S. Virgin Islands. Beachgoers should swim near lifeguards and follow local beach safety guidance.

Short Term(Today through Monday)

Issued at 235 AM AST Sat Jun 20 2026

Overnight, we had little or no rain as a drier air mass with moderate to high concentrations of Saharan Air Layer (SAL) remained over the Northeast Caribbean. The SAL limited nocturnal radiational cooling, leaving overnight temperatures in the upper 70s to the lower 80s across coastal and urban areas, and in the mid to upper 60s along the mountains. Most wind stations reported east to east-southeast winds of 5 to 15 mph, with fluctuations due to land breezes. However, some stations in the Northern US Virgin Islands reported northeast winds of 15 to 20 mph, with higher gusts.

Another day under hazy skies due to moderate to locally high concentrations of Saharan Dust Particles is expected across the US Virgin Islands and Puerto Rico today. This air mass will degrade air quality and visibility, possibly worsening respiratory symptoms in sensitive individuals. Additionally, the combination of warmer-than-normal maximum temperatures and available moisture will lead to dangerous heat indices, especially between 10 and 4 PM AST. This intense heat will affect many individuals sensitive to high temperatures, particularly those without effective cooling methods or sufficient hydration. Therefore, a Heat Advisory is in effect for coastal and urban areas in the USVI and PR.

Still, the strong surface high-pressure system across the Atlantic Ocean will tighten the local pressure gradient, resulting in breezy east-to-east-southeast winds across much of the region. This wind flow will transport occasional pockets of moisture, clouds, and showers across the USVI and PR's windward sectors. At the same time, daytime heating and local effects may trigger isolated to scattered afternoon convection across the interior and western portions of Puerto Rico, as well as downwind from the USVI. At this moment, looks like this weather pattern will repeat on Monday as a dry, dusty air mass filters in behind Father's Day's trailing tropical wave.

The NASA Dust Aerosol Optical Thickness guidance continues to indicate low to moderate concentrations of Saharan dust surrounding the Father's Day tropical wave. However, model guidance still suggests the best rain day for the region, although weather guidance has been overestimating rainfall over the past few days. That being said, this feature will increase moisture availability and enhance the potential for showers and thunderstorms, raising the risk of heavy rainfall, urban and small-stream flooding, and isolated flash flooding across portions of Puerto Rico and the U.S. Virgin Islands. Forecast confidence in the amount and intensity of rainfall remains somewhat uncertain. This uncertainty arises from the interaction between the moist air mass associated with the tropical wave and the drier, more stable air mass of the SAL surrounding the wave. We will continue to monitor the situation closely and update the forecast as our confidence grows.

Long Term(Tuesday through Saturday)

Issued at 235 AM AST Sat Jun 20 2026

The long-term pattern aligns towards a typical June weather conditions. Moisture content, relative humidity values, and mid- level temperatures are forecast to remain near normal values for this time of the year, supporting a fairly typical trade-wind pattern across the islands.

On Tuesday, a relatively stable air mass will prevail across the region. Passing trade-wind showers will continue to affect windward and eastern sections of the islands, while leeward areas experience mostly fair weather. Temperatures will remain seasonably warm, with highs in the upper 80s to low 90s across coastal and urban areas.

A tropical wave is forecast to move across the region on Wednesday and Thursday. While the wave will bring an increase in low-level moisture and result in a higher frequency of passing showers, model guidance suggests precipitable water values will remain near seasonal values. In addition, mid-level relative humidity values remain relatively low and temperatures near 500 mb stay close to normals, limiting the potential for widespread deep convection. As a result, periods of passing showers are expected, particularly across windward and eastern sections in the morning as well as the afternoon convection across western PR, but significant rainfall accumulations are not anticipated at this time.

By late Thursday and continuing through Saturday, a slightly drier air mass will filter into the region. This will promote a decrease in shower coverage and support a return to a more typical trade-wind weather pattern. Although isolated showers will remain possible across windward areas, mostly fair weather conditions are expected elsewhere. Temperatures will continue near seasonal normals, and no significant weather impacts are anticipated through the end of the forecast period.

AVIATION

(06Z TAFS) Issued at 235 AM AST Sat Jun 20 2026

A dense SAL will continue to lower visibilities across portions of the local flying area. Thus, expect HZ with VSBY dropping to near 6 SM, limited SHRA/-SHRA activity, without ruling them out. SHRA will form along the Cordillera and W-PR by this afternoon. Winds will be calm to light and variable overnight, and after 20/13z, expect E-ESE winds at 10-20 kt, with gusts up to 30 kt. A tropical wave will begin to reach the region, increasing the chance for SHRA/TSRA after 20/2350z.

MARINE

Issued at 235 AM AST Sat Jun 20 2026

A broad surface high pressure building over the Central Atlantic will continue to promote moderate to locally fresh easterly to east- southeasterly winds over the next several days. These conditions will create choppy seas across local waters and Caribbean passages; small craft should exercise caution. Meanwhile up to moderate and high concentrations of Saharan Dust will persist throughout the weekend and into the workweek, resulting in hazy skies, reduced visibility, and poor air quality. A tropical wave is expected to move across the Caribbean Sea Sunday into Monday, increasing the likelihood of showers and isolated t-storms across the regional waters.

BEACH FORECAST

Issued at 235 AM AST Sat Jun 20 2026

Breezy to locally windy conditions will maintain up to a moderate risk of rip currents during the next few days. Areas under a moderate risk of rip currents today and tonight include: northern, southeastern and southwester PR, as well as St. Croix, Vieques and Culebra. Life-threatening rip currents are possible in the surf zone at areas with a moderate risk. Even in areas with a low risk, life- threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. The moderate risk is forecast to spread across most of the local beaches, with most of them being under a moderate risk late tomorrow and into the workweek.

Concentrations of Saharan Dust will continue to move over the islands during the next several days, resulting in hazy skies, reduced visibility, and poor air quality. High heat indices will also persist during the period, sensitive groups should take necessary precautions. Residents and visitors are encouraged to follow the latest weather forecast, as afternoon showers and isolated thunderstorms can be expected this weekend and early next week, particularly near coastal areas of western/northwestern Puerto Rico.

FIRE WEATHER

Issued at 235 AM AST Sat Jun 20 2026

A Fire Danger Statement has been issued for today across portions of the coastal plains and hills of southern and western Puerto Rico, Vieques and St. Croix due to the combination of critically dry fuels, sustained winds of 15 to 20 mph with gusts up to 25 mph, and minimum relative humidity values in the low 50s or even in the 40s. These conditions will favor rapid wildfire ignition and extreme fire behavior, meaning any fires that develop will likely spread quickly and become difficult to contain. Outdoor burning is highly discouraged.

Fire and emergency officials should be aware that weather conditions are becoming more conducive for the ignition and spread of wildfires.

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.