textproduct: San Juan

KEY MESSAGES

Updated at 109 PM AST Sun May 31 2026

* Moderate concentrations of Saharan dust will continue to promote hazy skies and reduced visibilities through early next week, with higher concentrations this afternoon through Tuesday. Sensitive groups, including people with respiratory conditions, may experience discomfort and should follow medical recommendations.

* A tropical wave will continue to bring a brief surge in moisture content this afternoon, promoting an increase showers across the islands.

* Hot conditions are expected through early next week, particularly along the lower elevations and urban areas.

Short Term(This evening through Tuesday)

Issued at 109 PM AST Sun May 31 2026

Conditions today were variable across Puerto Rico, particularly over the eastern half of the island, where the day began mostly cloudy with periods of passing showers. Rainfall accumulations generally remained below 0.50 inches as the morning progressed. This cloud cover was associated with a tropical wave moving across the region gradually spreading westward, affecting the remainder of the island through the late morning and early afternoon. Across the U.S. Virgin Islands, skies remained partly cloudy with increasingly hazy conditions. A gradual increase in Saharan dust concentrations was also observed over Puerto Rico during the afternoon. Combined with available low-level moisture and mid to upper level instability associated with cooler temperatures and a trough aloft, these conditions supported the development of lightning over Culebra and over the Caribbean waters near Ponce.

Tonight, a dense Saharan Air Layer will continue to spread over the northeastern Caribbean. While a few brief trade-wind showers may move across windward sectors, rainfall activity is expected to diminish as moisture levels gradually decrease. Model guidance suggests precipitable water values near normals tonight before falling to below-normal levels through Tuesday.

The dominant weather feature through Tuesday will be the extensive Saharan dust plume becoming firmly established across the area. As this dry air mass settles over the islands, atmospheric moisture will steadily decrease, resulting in a more stable environment. Meanwhile, 500 mb temperatures are forecast to persist between -8 degrees Celsius and -10 degrees Celsius, maintaining relatively cool conditions aloft. Consequently, shower activity will become increasingly limited by Monday, with only isolated and brief trade- wind showers expected, mainly during the overnight and early morning hours. Rainfall accumulations should remain minimal across Puerto Rico and the U.S. Virgin Islands through Tuesday. The most noticeable impacts will be reduced visibility, deteriorated air quality, and warm to hot temperatures under generally sunny skies as dust concentrations peak across the local area.

Long Term(Wednesday through next Saturday)

Issued at 334 AM AST Sun May 31 2026

The long-term forecast remains on track with the arrival of a weak easterly disturbance and an accompanying surge of moisture. This will push precipitable water (PWAT) values up to a seasonal 1.50 to 1.75 inches. This setup will support a typical seasonal weather pattern, bringing passing showers to eastern Puerto Rico and the U.S. Virgin Islands during the morning hours, followed by afternoon convective activity across central and western Puerto Rico. However, despite the available moisture and low-level forcing, 500 mb temperatures will remain slightly above normal for the season at around -5C to -6C. This warmth aloft will limit instability and vertical cloud growth, capping the overall development of widespread thunderstorms.

At the mid-levels, a ridge will continue to promote drier air and stable conditions aloft throughout much of the period, favoring subsidence and limiting deep convection. By Thursday and Friday, following the passage of the easterly disturbance, PWAT values are anticipated to drop to near 1.00 inch, which is below normal for this time of year. Consequently, rainfall should become very limited and locally driven, with no impacts. This will result in a stretch of mostly dry, fair weather and sunshine across both Puerto Rico and the U.S. Virgin Islands.

By Saturday and into the weekend, the latest model guidance continues to suggest a transition toward a more unsettled weather pattern as a tropical wave approaches and an upper-level trough moves into close proximity. However, because this is at the end of the forecast period, uncertainty remains relatively high regarding the exact timing and amount of the rainfall.

Meanwhile, warm conditions are expected to persist throughout the entire long-term forecast. Seasonal to slightly above-normal temperatures will hold steady through the weekend, with maximum temperatures expected to range from the mid to upper 80s degrees Fahrenheit along coastal and urban areas, and from the upper 70s to low 80s across the higher elevations.

AVIATION

(18Z TAFS) Issued at 109 PM AST Sun May 31 2026

VFR conditions across all terminals. However, brief MVFR conds over TJBQ and TJPS after 31/18Z -TSRA/SHRA can develop over interior to W-NW PR through around 31/22Z. Over windward sectors, occasional limited VCSH are possible. HZ prevail during the next 24 to 48 hrs due to saharan dust with reduced VIS (btw 6 to 8 SM) possible. ESE winds at 10 to 16 kt, with higher gusts and sea breeze variations, decreasing after 31/23z.

MARINE

Issued at 109 PM AST Sun May 31 2026

No changes were introduced to the marine forecast. The tropical wave continues to move across the Caribbean Basin, with isolated to scattered showers and thunderstorms affecting regional waters. Small craft should exercise caution as thunderstorms may bring gusty winds and lightning that may result in hazardous conditions. As mentioned in the previous discussion, the Azores high will continue to promote moderate to fresh east-southeasterly winds this week, which may lead to choppy seas across regional waters. A dense plume of Saharan Dust will gradually filter this afternoon, resulting in hazy skies, reduced visibility, and a deterioration of air quality throughout the week.

BEACH FORECAST

Issued at 109 PM AST Sun May 31 2026

The low risk of rip currents should continue for the rest of today across the islands. However, beachgoers should take into account that isolated, stronger rip currents may occur, particularly near groins, jetties, reefs, and piers. As winds are expected to gradually strengthen by tomorrow, Monday, the risk should increase to moderate for most beaches across the islands and persist for the rest of the week. Beachgoers must exercise caution, as life- threatening rip currents are possible along the surf zone.

In addition to rip currents, beachgoers are encouraged to remain weather alert as showers and thunderstorms associated with a tropical wave near the area may move near coastal areas of the islands this afternoon. Moderate to high concentrations of Saharan Dust will gradually filter into the region and persist throughout the week, peaking this afternoon through Tuesday. These concentrations may result in hazy skies, reduced visibility, and poor air quality.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.