textproduct: San Juan

KEY MESSAGES

Issued at 127 PM AST Sun Nov 8 2026

* Slow-moving showers and isolated thunderstorms will keep the potential for urban and small-stream flooding risk this afternoon, especially across interior and eastern Puerto Rico, including the San Juan metro area.

* Scattered showers close to the U.S. Virgin Islands could produce periods of brief, but heavy rainfall over land areas today.

* A northerly to northeasterly swell will maintain a high risk of life- threatening rip currents along exposed northern beaches of Puerto Rico and portions of Culebra through Monday afternoon. * By mid-week, a more stable weather pattern is expected to prevail across the region. Afternoon thunderstorms are expected each day across the interior to western and northwestern PR.

Short Term(This evening through Tuesday)

Issued at 127 PM AST Sun Nov 8 2026

The local islands remain situated within a region of relaxed winds under a weak pressure gradient, associated with an approaching col area from the west. The 08/12Z TJSJ upper air sounding indicated a predominantly westerly steering flow from the surface to 3 km at only 5 knots. This flow may fluctuate between WNW and WSW during the afternoon, modulated by the interaction between low pressure northeast of the Caribbean and weak high pressure to the east (with the local islands currently positioned just east of the col). A plume of low-level moisture situated between these systems will persist throughout the short-term period, maintaining precipitable water (PWAT) values between seasonal and above seasonal levels (1.8 to 2.2 inches). This moisture plume is supporting some convective bands across both the local Atlantic and Caribbean waters. Periodic activity will affect the islands from time to time, particularly the U.S. Virgin Islands (USVI), resulting in minor impacts such as ponding of water on roadways and in poorly drained areas.

A weak upper-level ridge is maintaining some dry air and stability aloft (above 500 hPa). However, near- to above- normal moisture extends through 500 mb, accompanied by 500 mb temperatures of -4.4 to -5.0 C. These factors, combined with strong diurnal heating and enhanced orographic convergence under light steering winds, will trigger another active afternoon. Scattered showers and isolated thunderstorms will initiate across the central to eastern interior of Puerto Rico, with the possibility of subsequently drifting into eastern sections, including the east coast, the northeast (including the San Juan metropolitan area), and potentially the southeast. Because of the very weak steering flow, a low to moderate chance (30 to 50%) exists for rainfall accumulations to exceed 2 inches locally, particularly from the interior to the northern slopes of Puerto Rico. Given saturated soils from recent rainfall, an elevated flood threat is expected, with urban and small stream flooding, rapid rises along small rivers, mudslides or even landslides in areas of steep terrain, and the possibility of isolated flash flooding. Activity should diminish around sunset, with isolated lingering showers persisting into the early evening.

Tonight into Monday, isolated passing showers remain possible across the USVI, and some may reach southern and southeastern Puerto Rico. On Monday, winds will remain weak and shift to more southerly as the col axis crosses very close to or directly over the local area. Plentiful moisture, along with diurnal heating and sea breeze convergence, will trigger another round of afternoon showers and isolated thunderstorms across the interior to northern sections of Puerto Rico. On Tuesday, southerly to southeasterly steering flow will sustain afternoon convection focused primarily over the interior to northern half of Puerto Rico. This will maintain the threat for urban and small stream flooding each afternoon across those areas. Slightly drier conditions are expected for the USVI on Tuesday as the moisture plume shifts northward late Monday into Tuesday, though isolated passing showers cannot be ruled out.

Maximum heat indices between 100 and 106 degrees Fahrenheit are expected each day across coastal and urban areas, prior to the onset of afternoon convective activity. Individuals sensitive to heat should take appropriate precautions to mitigate heat- related risks.

Long Term(Wednesday through next Saturday)

Issued at 352 AM AST Sun Nov 8 2026

The long term period will be mainly characterized by variable conditions at the beginning, becoming slightly more stable by the end of the week. At the synoptic level, a surface high pressure will build across the western Atlantic by Wednesday, gradually shifting eastward into the central Atlantic during the remainder of the period. This will result in easterly winds by midweek, becoming east to southeasterly from Thursday through at least Saturday, before backing to the east once again on Sunday. Winds are expected to follow an increasing trend. Compared to previous days, when winds will remain light, they should increase to around 12 to 16 kt overall during the long-term period.

By Wednesday and Thursday, the latest model guidance suggests the influence of shortwave troughs near the Caribbean. Moisture content across the region is expected to remain near seasonal levels, with mean precipitable water values fluctuating between 1.7 and 1.9 inches. However, global models show some disagreement, with the GFS indicating higher values and the ECMWF showing lower values. Relative humidity in the 850 to 700 mb layer is expected to remain generally near seasonal levels, while the 700 to 500 mb layer should also maintain sufficient moisture to support cloud and precipitation development. The passage of shortwave troughs during this period could provide marginal dynamical support for upward motion. Combined with daytime heating and local effects, these features could contribute to periods of showers and possibly isolated thunderstorms, particularly during the afternoons across northern to northwestern portions of Puerto Rico. As a result, flooding will remain in the forecast across these areas (Level 1 of 4), indicating the potential for flooding in urban areas, along roads, and near small streams.

From Friday onward, moisture conditions are expected to remain relatively favorable, although a gradual decrease in mid-level moisture may occur as a ridge builds across the region. Precipitable water values are generally expected to remain near or below 1.9 inches, which is close to seasonal levels. However, the development of a mid-level ridge should promote greater atmospheric subsidence and potentially limit vertical development, despite the persistence of moisture in the lower levels. Additionally, models suggest a warming trend in 500 mb temperatures. Consequently, while isolated to scattered showers may continue, particularly due to local effects, precipitation activity could become more localized compared to Wednesday and Thursday.

Throughout the period, current model guidance suggests that 925 mb temperatures will remain near the 75th percentile or two standard deviations above normal, based on climatology for the month of November. Therefore, before rainfall develops, heat indices are expected to be elevated, primarily affecting individuals who are particularly sensitive to heat. Residents and visitors are encouraged to remain hydrated and continue monitoring weather conditions, as forecast updates and adjustments become available.

AVIATION

(18Z TAFS) Issued at 127 PM AST Sun Nov 8 2026

Mainly VFR conds expected through 09/18Z. Afternoon SHRA/isolated TSRA over interior PR may affect TJSJ/TJBQ, and activity across surrounding waters will affect IST/ISX thru 08/23Z, producing brief MVFR conds and mtn obsc. Brief IFR possible in +SHRA/TSRA. VCSH possible at USVI, possibly moving over them. SHRA/TSRA will diminish after sunset, with mostly VFR overnight and isolated passing SHRA. Light W/WSW winds with sea breeze influence, then shifting to E-ESE at 5-10 kt after 09/14Z. Locally gusty and erratic winds possible near TSRA.

MARINE

Issued at 127 PM AST Sun Nov 8 2026

Nearshore buoys this afternoon show seas around 4 to 5 feet along northern and western Puerto Rico, with a north-northeasterly swell at 11 to 13 seconds, while Ponce reports seas near 1 foot. The swell will maintain offshore Atlantic seas at 5 to 6 feet through tonight, warranting caution for small craft. Seas will gradually subside Monday as the swell decays.

As low pressure northeast of the region moves eastward and high pressure builds across the western Atlantic, light winds will transition to an easterly flow Monday, strengthening to 10 to 15 knots by Tuesday. Atlantic seas will generally range from 4 to 5 feet thereafter, while Caribbean seas remain at 2 to 3 feet through Tuesday before increasing to 3 to 4 feet late Wednesday. Showers and isolated thunderstorms may produce locally higher winds and seas.

BEACH FORECAST

Issued at 127 PM AST Sun Nov 8 2026

A northerly to northeasterly swell is impacting the Atlantic water and local passages, producing breaking waves of 5 to 8 feet along exposed northern and northeastern beaches of Puerto Rico, including portions of Culebra. The beaches of Rincon and Aguada will also experience some of this swell energy. The high risk of life- threatening rip currents will remain in effect through at least tomorrow (Monday) afternoon. Rip currents are also possible along the beaches of Vieques, the U.S. Virgin Islands and along eastern and western Puerto Rico. Avoid swimming at beaches with a high rip current risk.

Thunderstorms will pose an additional hazard, with isolated thunderstorms possible through midweek particularly across the western, northern and eastern coastal areas of Puerto Rico. If thunder is heard, leave the beach and seek shelter in a substantial building or enclosed vehicle.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Monday afternoon for PRZ001-002- 005-008-010-012.

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