textproduct: San Juan

KEY MESSAGES

Updated at 308 PM AST Sun Jul 26 2026

* A more unsettled weather pattern is forecast for tonight into Monday as a tropical wave and an upper instability move across the area. Therefore, there is a limited to elevated flooding threat along the northwestern side for tomorrow.

* Warm conditions will persist today under an east-southeasterly wind flow. Therefore, peak heat indices could approach 100F TO 110F across coastal and urban areas, particularly north- central Puerto Rico.

* A moderate risk of rip currents remains in effect for the northern and eastern exposed beaches of Puerto Rico, Culebra, Vieques, and St. Croix.

* For the U.S. Virgin Islands, the potential for showers starts late tonight into early on Monday with periods of passing showers and some localized thunderstorms in the waters.

Short Term(This evening through Tuesday)

Issued at 308 PM AST Sun Jul 26 2026

Current Satellite Derived Precipitable Water (PWAT) values range between 1.34 and 1.65 inches across most of the region, with the exception being St. Croix with PWAT values around 1.70 inches and gradually increasing as the moisture field from a tropical wave continues to approach the islands. Lingering Saharan Dust and subsidence ahead of this tropical wave promoted a tranquil, albeit warm to hot and hazy over some sectors, morning and early afternoon. Diurnal heating, local orographic effects and sea breeze convergence have quickly triggered convective shower and t-storm activity within the past hour over interior to western Puerto Rico, a limited flooding risk continues over those areas this afternoon and evening although available moisture should stay below 800 mb. Ponding of water in roads and poorly drained areas with a chance of urban and small streams flooding and locally strong t-storms continue to be forecast. Shower activity can also still develop downwind of the local islands and El Yunque. A Heat Advisory also remains in effect for coastal and lower elevation areas of the islands through 5 PM as heat indices have reached the 100s to even the low 110s.

The leading edge of deeper tropical moisture (interacting with a mid- to upper-level trough that is over the islands and will persist through the period) will support an increase in scattered showers and isolated t-storms over the region. The moisture field from the wave and related showers and t-storms will arrive from the southeast and reach St. Croix first tonight, increasing PWAT values to 1.90 in. As the tropical wave advances west- northwestward across the northeastern Caribbean, moisture levels and atmospheric instability will continuously rise through Monday and Tuesday. Deep tropical moisture, above normal PWAT that can reach above 2 inches and increasingly favorable conditions for shower and t-storm development will continue overspreading the region tonight through Tuesday evening PWAT values will continue above normal and reach above 2 inches. This evolving meteorological pattern will support periods of scattered to numerous showers along with isolated to scattered thunderstorms; this convective activity is expected to be most pronounced during the overnight and morning hours on Monday, and during the afternoon hours on both Monday and Tuesday under an east-southeast steering flow. Therefore, a heightened risk of flooding is expected for both days. The probability of flooding will increase in urban zones and small streams, while a restricted possibility for localized flash flooding remains in sectors experiencing the most severe and enduring convection.

Forecast 925 mb temperatures remain anomalously warm alongside the anticipated rainfall threat. Consequently, sectors with sparse rainfall are anticipated to experience above-normal daytime maximums and unseasonably warm overnight minimums. These factors, in tandem with surging tropical moisture, will encourage elevated to potentially significant heat impacts across parts of the islands.

Long Term(Wednesday through next Saturday)

Issued at 308 PM AST Sun Jul 26 2026

Recent model guidance continues to suggest abundant moisture across Puerto Rico and the U.S. Virgin Islands as a tropical wave moves through the region early in the period. The latest precipitable water (PWAT) values are near 2.0 inches, reflecting normal to above- normal moisture for this time of year. Under this scenario, scattered trade wind showers remain possible during the morning, followed by afternoon showers and isolated thunderstorms across central and northwestern Puerto Rico driven by daytime heating and local effects.

However, these conditions will be short-lived as a drier air mass quickly moves into the area by Wednesday night. At the surface, a strengthening high-pressure system will tighten the pressure gradient, promoting breezy conditions through the rest of the period. Stability aloft will be further supported by a building mid- to-upper level ridge, limiting overall shower activity across the islands through the second half of the week as PWAT values drop below normal to 1.25-1.30 inches. Nonetheless, quick patches of moisture embedded in the trade winds will bring occasional fast- moving showers with minimal to no impact. Moisture levels should see a slight increase by late Saturday into Sunday as another tropical wave approaches the region. Near to above-normal temperatures will persist daily, with daytime highs reaching the upper 80s to low 90s across coastal and urban areas.

AVIATION

(18Z TAFS) Issued at 308 PM AST Sun Jul 26 2026

VFR conditions prevail through this evening with easterly winds at 15 to 20 kts with gusts up to 30 kts will diminish after 26/23Z, then pick up again from the east-southeast around 15 mph, with higher gusts and stronger near SHRA/TSRA at around 27/12Z. Afternoon SHRA/TSRA across interior to western PR will continue to affect the vicinity of TJPS and TJBQ through 26/23Z, bringing brief MVFR/IFR conditions and mountain obscurations. Overnight increasing SHRA/TSRA will affect TIST/TISX/TJSJ/TJPS as a tropical wave approaches and continues moving eastward, creating an unstable and wet pattern along with possible brief MVFR/IFR conditions.

MARINE

Issued at 308 PM AST Sun Jul 26 2026

Surface high pressure across the Central Atlantic will maintain moderate easterly winds across the regional waters through Sunday, ranging between 10 and 15 knots with gusts up to 20 knots at least until tonight before the arrival of the axis of a tropical wave. Therefore, seas will generally remain between 2 and 4 feet across protected waters and up to 5 feet across open Atlantic and Caribbean waters. Marine conditions will begin to deteriorate late tonight into Monday as an approaching tropical wave interacts with an upper-level cut-off low. This system will bring a significant increase in passing showers and thunderstorm activity across the regional waters, starting in the Anegada Passage and USVI waters before spreading west. Mariners should expect sudden localized gusts in excess of 25 knots, frequent lightning, and locally elevated seas near the strongest thunderstorms.

BEACH FORECAST

Issued at 308 PM AST Sun Jul 26 2026

A moderate risk of rip currents will continue through the remainder of the day for the northern, eastern, and southeastern beaches of Puerto Rico, as well as Culebra, Vieques, and St. Croix. While breaking wave heights will remain relatively low at 2 to 4 feet. For tomorrow, a decrease in winds will lead to a low risk of rip currents; however, other threats, such as thunderstorm activity, might result in hazardous beach conditions.

The moderate risk of rip currents returns on Tuesday.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013.

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

AM...None.