textproduct: San Juan

KEY MESSAGES

Issued at 202 PM AST Fri Jun 26 2026

* An upper level low will induce a surface trough that will cross the islands tomorrow, promoting lighter winds as well as a limited flooding and lightning risk.

* Warm weather conditions should prevail across the islands, generating elevated heat threat.

* Approaching tropical wave, increasing the flooding potential on Monday.

Short Term(This evening through Sunday)

Issued at 202 PM AST Fri Jun 26 2026

Tonight, Saharan dust concentrations will continue to decrease as the Saharan Air Layer (SAL) exits the region, resulting in improving visibility and air quality. Overnight temperatures will cool slightly more than in previous nights, with lows falling into the 70s across the coastal and urban areas and into the 60s across the higher terrain. Winds will gradually weaken and become east- northeasterly. Late tonight, a surface trough associated with an upper-level low will approach the northeastern Caribbean, gradually increase moisture and lead to a higher frequency of passing showers, mainly across the local waters, the U.S. Virgin Islands, and eastern Puerto Rico in the early morning hours.

On Saturday, the approaching surface trough will increase moisture across the region, with precipitable water values rising to around 1.8 inches (still near normal values for this time of the year). Passing showers will become more frequent during the morning across the U.S. Virgin Islands and eastern Puerto Rico before shifting inland during the afternoon. As winds become east to east- southeasterly, the most active convection is expected across the interior, western, and northwestern sections of Puerto Rico, with additional shower bands developing downstream of the U.S. Virgin Islands and El Yunque. Although atmospheric instability remains low, the combination of deeper moisture and weak steering flow will support slow-moving showers and isolated thunderstorms capable of producing locally heavy rainfall. The primary impacts will be ponding of water on roads and in poor drainage areas, along with isolated urban and small-stream flooding, especially during the afternoon.

On Sunday, a drier air mass will return behind the departing trough, leading to a more typical summertime weather pattern. Expect a few passing showers across windward areas during the morning, followed by isolated afternoon showers over the interior and western Puerto Rico. Breezy east to east-southeast winds will also transport a low concentration of Saharan dust back into the region. Despite the slightly drier conditions, above-normal temperatures will maintain an elevated heat risk across the lower elevations. Moisture associated with an approaching tropical wave is forecast to begin increasing late Sunday night, signaling a return to wetter conditions early next week.

Long Term(Monday through next Thursday)

Issued at 329 AM AST Fri Jun 26 2026

During the long-term period, a surface high pressure over the eastern Atlantic will maintain a southeasterly low-level flow across the region through the workweek. By Monday into Tuesday, current guidance continues to suggest that moisture associated with a tropical wave will approach the Caribbean Basin, resulting in a gradual increase in deep-layer moisture across the local islands. As a result, precipitable water (PWAT) values should increase to near- normal or slightly above-normal levels, ranging from around 1.7 to nearly 2.0 inches based on climatological averages. In addition, relative humidity within the 700-500 mb layer is forecast to rise to near or above seasonal values. This increase in moisture should enhance rainfall potential, resulting in greater coverage of showers and afternoon convection, with localized ponding of water possible on roads and in poorly drained areas. Cooler temperatures aloft associated with lower 500 mb temperatures may also provide additional support for convective development during the afternoon hours. However, lingering low to moderate concentrations of Saharan dust may limit convective coverage to some extent, introducing uncertainty in the overall coverage and intensity of rainfall. Also, low to slightly moderate concentrations of Saharan Dust is expected to remain present, and its interaction with the incoming moisture introduces some uncertainty to the forecast. By mid week into the end of the week; particularly Thursday and Friday, drier air is expected to filter into the region (PWAT below 1.5 inches), leading to a gradual decrease in rain chances.

One of the primary weather concerns throughout the period will be the persistence of warm to hot conditions. Forecast guidance indicates 925 mb temperatures around two standard deviations above normal, particularly on Monday, when the combination of above-normal temperatures and increasing moisture will promote hot and muggy conditions. Daytime high temperatures are expected to reach the upper 80s to lower 90s, with heat index values potentially exceeding 100 degrees F, especially across coastal and urban areas. As a result, an elevated heat risk is likely to persist through much of the forecast period. Residents and visitors are encouraged to stay hydrated, wear lightweight and loose-fitting clothing, and take frequent breaks in shaded or air-conditioned areas if spending extended periods outdoors.

AVIATION

(18Z TAFS) Issued at 202 PM AST Fri Jun 26 2026

VFR conditions, although HZ will continue through 26/23Z. Easterly winds decreasing after 26/23z to around 5 to 10 kt. VCSH possible after 27/03Z.

MARINE

Issued at 202 PM AST Fri Jun 26 2026

A surface trough will move north of the region late tonight, gradually weakening the local pressure gradient and winds, becoming light to moderate from the northeast on Saturday. Showers and isolated thunderstorms associated with the trough will likely move across the local waters and Caribbean passages, which may create locally hazardous conditions for small craft. As the trough moves westward, the broad surface high pressure over the Central Atlantic will dominate the wind pattern, increasing local pressure gradient and winds, becoming moderate to locally fresh from the southeast. The moderate concentrations of Saharan Dust will continue to diminish tonight, though low concentrations may filter into the region by Sunday.

BEACH FORECAST

Issued at 202 PM AST Fri Jun 26 2026

The beach forecast remains on track. Most beaches across Puerto Rico and the U.S. Virgin Islands remain under a moderate risk of rip currents, with breaking waves between 2 and 4 feet. Although theres no high risk of rip currents, residents and visitors must exercise caution if going to a beach under a moderate risk, as life- threatening rip currents remain possible along the surf zone. As mentioned in previous discussions, winds will weaken due to a surface trough approaching the local area tonight, lowering the risk of rip currents for tomorrow, Saturday. Nevertheless, beachgoers should be aware that, under a low risk, life-threatening rip current can occur in the vicinity of groins, jetties, reefs, and piers. In addition to rip currents, showers and isolated thunderstorms associated with the trough may move near coastal areas of the islands, beachgoers must remain weather alert and exercise caution. By Sunday, winds will gradually strengthen, and the risk of rip currents should be upgraded to moderate over exposed beaches, spreading across the islands early next week. Saharan Dust concentration will gradually decrease tonight, with low concentrations arriving by Sunday.

FIRE WEATHER

Issued at 329 AM AST Fri Jun 26 2026

A Fire Danger Statement has been issued for today (from 10 AM to 4 PM AST) across portions of the southern coastal plains of Puerto Rico due to the combination of critically dry fuels, high KBDI values, sustained winds of 15 to 20 mph with gusts up to 30 mph, and possible minimum relative humidity values in the 40s to low 50s as dry air with high concentrations of Saharan Dust continue moving over the region. Prolonged rainfall deficits, abnormally dry to severe drought conditions, and critically dry fuels also continue. 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. With more E-NE steering flow, shallow afternoon convection could provide some relief to the SW coastal plains today.

SJU WATCHES/WARNINGS/ADVISORIES

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