textproduct: San Juan

KEY MESSAGES

Issued at 200 AM AST Wed Oct 7 2026

- Increasing moisture associated with a nearby tropical wave will promote a wetter and more active weather pattern today. As a result, there is an increased chance of periods of heavy rainfall and thunderstorms. A limited to elevated flood risk will persist across the islands today.

- On Thursday, lingering moisture and southeast flow will likely support hot and humid conditions, along with afternoon showers and thunderstorms across interior and western areas of Puerto Rico.

- A more seasonal weather pattern is expected to return by the end of the week. From Sunday into early next week, models suggest that a more unstable atmosphere may return. Stay tuned to the forecast.

- A moderate risk of rip currents is expected through Thursday night mainly along portions of the north- to southeast-facing beaches of the islands, then a low risk is forecast for Friday and continuing through the weekend.

Short Term(Today through Friday)

Issued at 200 AM AST Wed Oct 7 2026

The overnight hours kicked off the short term period with an active period of weather. The humidity associated to a tropical wave filtered its way into the region bringing above average precipitable (PWAT) values to the US Virgin Islands and eastern Puerto Rico. This lead to the development of showers across the offshore waters, US Virgin Islands and the eastern half of Puerto Rico. While significant accumulations have not been registered by the radar, the activity will continue throughout the day. Where recurring rainfall and downpours occur the flooding risk will be moderate. This means that flooding in urban areas, roads, small streams and washes, as well as low chance for isolated flash floods is possible. Convection has already induced wind gusts up to 30 mph in portions of the US Virgin Islands and southern Puerto Rico.

The rest of today should be dominated by a variable weather pattern associated to the wave passage over the islands. While a couple of mid-level high pressure systems to the north of the CWA are acting to limit the development of deep convective cells by warming the layer and weakening the lapse rates at these levels, the wave will provide sufficient instability for the development of widespread showers and localized thunderstorms. Model guidance indicates increased values of PWAT and column RH which will further aid in the development of convective activity. A surface high pressure system to the north of the region is currently promoting breezy ESE conditions which will further act to advect warm and moist air from the wave into the region. The winds will gradually reduce into the afternoon which will allow convection to linger which may aid in the development of flooding wherever persistent recurring rainfall occurs. Given the amount of widespread cloud coverage expected for the day the heat risk remains limited. Individuals are invited to remain informed of the evolving weather conditions and forecasts as they become available.

Similar favorable features will be present on Thursday. Lingering moisture from the wave should provide sufficient instability for the development of showers and thunderstorms. The focus of the activity for this day will be on the northwest portion of Puerto Rico where a moist vertical column will prevail. Nonetheless, breezy ESE conditions will return aiding in the development of streamers from el Yunque and the smaller islands, which will predominantly affect the US Virgin Islands and eastern Puerto Rico during the afternoon, and advective showers over the night and morning. Given that convection for the day will be more localized and have less cloud coverage and with 925 mb temperatures 2 standard deviations above average for the season, the heat risk for Thursday is elevated. This level of heat can affect most individuals sensitive to heat, especially those without effective cooling and adequate hydration. We recommend limiting outdoor activities and staying hydrated.

By Friday a mass of drier air will filter into the region promoting predominantly fair weather. The column will also be dominated by drier mid-to-upper levels further inhibiting the development of convection. The mid-level high pressure systems will continue enhancing warming and weakening of the lapse rates at these levels. This will act to cap convection and limit the development of deep convection. With the low-level high pressure system moving further north the steering flow is expected to shift to be from the ENE bringing drier cooler air to the islands. The activity that does develop will thus be driven by local effects and should be focused on the western interior and southwestern region of Puerto Rico. This breezy northeasterly windflow should also provide some respite to the warm conditions across the islands, hence a limited heat risk is expected for the day.

Long Term(Saturday through Wednesday)

Issued at 200 AM AST Wed Oct 7 2026

Latest global model guidance indicates a highly unstable pattern unfolding across the northeastern Caribbean as we move through the weekend and into early next week. While Saturday begins with recovering moisture supporting seasonable weather conditions, a potent upper-level cut-off low is forecast to dig southward from the central Atlantic and stall over the local islands through the first part of the week. As this feature settles over the region, mid-level temperatures at 500 mb will drop from around -5 degrees Celsius on Saturday down to -7/8 degrees Celsius between Monday and Wednesday. This anomalous cooling aloft will produce steep mid-level lapse rates and generally unstable conditions. Additionally, a favorable 250 mb jet will provide strong upper-level divergence and excellent ventilation that can support deep, organized convection.

Alongside these favorable upper-level dynamics, a deep plume of tropical moisture will pool across the region. Precipitable water values, which begin the period around 1.80 inches, are projected to climb and remain near or above 2.00 inches from Sunday through Wednesday. The combination of this deeply saturated atmospheric column with deep instability and strong upper-level lift can produce multiple rounds of heavy showers and intense thunderstorms. Consequently, there will be an elevated threat of urban and small- stream flooding, localized flash flooding, strong gusty winds, and frequent lightning strikes. While daytime heating and local effects will still focus the most intense, slow-moving convection over the interior and western portions of Puerto Rico, the broad synoptic forcing will also bring periods of locally heavy rainfall and strong thunderstorms to the USVI and eastern PR.

AVIATION

(06Z TAFS) Issued at 200 AM AST Wed Oct 7 2026

Mainly VFR conditions thru the forecast period, but intermittent periods of MVFR/IFR conds will occur today as a tropical wave brings the potential for SHRA/TSRA across most TAF sites. This morning mainly across USVI and TJSJ/TJPS sites, then likely spreading into TJBQ later today. Expect locally reduced VSBY, LTG, lower CIGS, and gusty/VRB winds near stronger rain activity. ESE winds 10-15 kt with some periods of higher gusts, then becoming light/VRB aft 07/23Z.

MARINE

Issued at 200 AM AST Wed Oct 7 2026

Surface high pressure continues to move east across the central Atlantic while a frontal boundary advances across the western Atlantic, north of the local area. The interaction between the high pressure and an incoming tropical wave will tighten the pressure gradient through this morning, generating choppy conditions primarily across Caribbean waters and local passages. The wave will also bring increased shower and thunderstorm activity, accompanied by locally strong gusty winds and higher seas. As the wave departs late Wednesday into Thursday, another high-pressure system will move across the western Atlantic, maintaining mainly gentle to moderate easterly trade winds.

BEACH FORECAST

Issued at 200 AM AST Wed Oct 7 2026

The combination of a small northerly swell and a tropical wave moving across the area will maintain a moderate risk of rip currents today along the north-, east- and south-facing beaches of Puerto Rico, as well as Vieques, Culebra, and the U.S. Virgin Islands. The moderate risk continues tomorrow for north- and east- facing beaches, as well as most of the USVI.

The tropical wave will increase shower and thunderstorm activity through tomorrow, resulting in an increased lightning risk at most beaches. Locally gusty winds are also possible near thunderstorms.

SJU WATCHES/WARNINGS/ADVISORIES

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