textproduct: San Juan

KEY MESSAGES

Updated at 315 PM AST Mon Jul 27 2026

* Moisture associated with a tropical wave will increase the potential for showers and thunderstorms through Tuesday, elevating the risk of urban and small-stream flooding, particularly across the interior and western Puerto Rico during the afternoon hours.

* Moisture will decrease by Wednesday, reducing the flooding threat while winds continue to increase.

* A Heat Advisory remains in effect through this afternoon. Warm to hot conditions will persist across Puerto Rico and the U.S. Virgin Islands through the rest of the week. Additional Heat Advisories or even Extreme Heat Warnings may be needed in the coming days, especially in areas where rainfall remains limited.

* Moderate concentrations of Saharan dust will gradually return tomorrow, Tuesday, and persist through at least early Friday.

Short Term(This evening through Wednesday)

Issued at 315 PM AST Mon Jul 27 2026

The moisture field, related to a tropical wave moving over the region, with precipitable water (PWAT) values around 2 inches has remained mostly over the southeastern and eastern waters and over the USVI, Vieques and Culebra. PWAT values over northwestern Puerto Rico have reached similar values due to recently formed t-storms. Subsidence ahead of this tropical wave promoted a generally fair but warm to hot morning and early afternoon, with the exception of early morning showers over the eastern region. These showers over the eastern region were passing as the bulk of showers and t-storms related to the wave stayed over the Caribbean waters during the early morning. The tropical wave interacting with an upper level trough, diurnal heating (with highs in the low 90s), local orographic effects and sea breeze convergence have resulted in convective shower and t-storm activity within the past hours over interior, western and northwestern Puerto Rico, sustaining a flooding risk. These t-storms have resulted in frequent lightning and heavy rain with rainfall totals between 1.5 to around 2 inches being observed. While these t-storms can persist and spread to surrounding areas during the afternoon, convective 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 once again reached the 100s to even the low 110s.

Through at least tomorrow, Tuesday, the interaction between this lingering tropical wave, and its moisture field (PWAT values around 1.90 to 2 inches), and the upper-level trough will continue to affect the region. As the wave advances west-northwestward across the northeastern Caribbean, tropical moisture and atmospheric instability will stay above normal through tomorrow, maintaining the possibility of bands of showers and t-storms reaching the region and convective showers and t-storms developing during the afternoon at interior to W-NW Puerto Rico and downwind of El Yunque and the local islands, sustaining a flooding risk. Additionally, stronger t- storms may produce frequent lightning and locally gusty winds. As the surface high over the Atlantic strengthens, ESE flow will become breezy tomorrow to locally windy on Wednesday. A drier air mass is forecast to spread across the region by Wednesday afternoon, leading to a gradual reduction in moisture levels, with precipitable water values dropping to below normal values. Furthermore, the return of pulses of Saharan dust is anticipated to bring hazier skies and diminish the likelihood of t-storm and shower development. 925 mb temperatures are forecast to remain above normal tomorrow and Thursday. Due to this, areas with little rainfall are anticipated to experience above-normal highs and warm overnight lows under persistent east-southeast flow. These factors, along with increased moisture tomorrow, will continue to result in elevated to potentially significant heat risks across parts of the islands.

Long Term(Thursday through Monday)

Issued at 305 AM AST Mon Jul 27 2026

The latest model guidance continues to suggest the arrival of a drier air mass across the region, dropping precipitable water values below normal to around 1.30 to 1.40 inches on Thursday. Along with this drier air, NASA GEOS-5 model guidance indicates low-to-moderate concentrations of Saharan Dust arriving through the first half of the period.

Strengthening surface high pressure over the central Atlantic will create a tight pressure gradient, bringing breezy to locally windy east-southeast winds through Saturday. Aloft, a mid-to-upper-level ridge will promote stable conditions, limiting widespread shower activity. However, the forecast remains on track for patches of low- level moisture embedded in the trade winds to move across the area. This will bring passing showers, particularly over the windward portions of the islands during the morning hours. In the afternoons, this moisture combined with daytime heating and local effects could trigger shower activity along the interior and northwestern portions of Puerto Rico.

By late Sunday into Monday, an approaching tropical wave will increase moisture alongside the potential for widespread showers and thunderstorms. Elevated temperatures will persist through the period, driven by normal to above-normal temperatures at the 925 mb level, with daytime highs reaching the upper 80s to low 90s across coastal and urban areas. Residents and visitors are encouraged to monitor forecasts and stay updated on changing conditions as the week progresses.

AVIATION

(18Z TAFS) Issued at 315 PM AST Mon Jul 27 2026

Mainly VFR conditions will prevail through this evening with ESE winds at 15 to 20 kts, and gusts up to 25 kts (higher near TSRA), these winds will diminish after 27/23Z before picking up again from the ESE at 15 to 20 kts at around 28/12Z. As a tropical wave moves over the region, afternoon SHRA/TSRA across interior to western PR will continue to affect mainly the vicinity of TJPS and TJBQ through 27/23Z, bringing brief MVFR/IFR conditions and mountain obscurations. Bands of SHRA/ and possible TSRA can also reach eastern terminals through the period.

MARINE

Issued at 315 PM AST Mon Jul 27 2026

Moisture associated with a tropical wave will increase the potential for showers and thunderstorms through Tuesday. Gentle to moderate east to east-southeast winds will continue through the rest of today, becoming moderate to fresh Tuesday afternoon into Wednesday as high pressure strengthens over the Atlantic, tightening the pressure gradient. These winds will maintain choppy seas across portions of the Atlantic waters, offshore Caribbean waters, and the local passages, with seas up to 6 feet expected in localized areas from midweek through at least the end of the week.

BEACH FORECAST

Issued at 315 PM AST Mon Jul 27 2026

Under light winds, an overall low risk of rip currents is expected tonight. Caution is always recommended, as even when the risk is low, life-threatening rip currents can occur near reefs, jetties, groins, and piers. As winds begin an increasing trend on Tuesday, a moderate risk of rip currents is forecast across northern Puerto Rico. Then, easterly winds will continue to increase as high pressure over the Atlantic strengthens from Wednesday onwards, becoming breezy to locally windy. As a result, the moderate risk of rip currents will expand to most beaches of Puerto Rico and the U.S. Virgin Islands. Life-threatening rip currents will remain possible, exercise caution. Additionally, warm to hot conditions will prevail, mainly across coastal and low-elevation areas. Stay hydrated and take frequent breaks in the shade.

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.