textproduct: San Juan

KEY MESSAGES

Issued at 425 AM AST Fri Oct 9 2026

- Drier conditions are forecast for today, as available moisture decreases. Afternoon convection and a limited flooding risk is still forecast as ESE winds become ENE during the afternoon.

- A limited heat risk is forecast for Puerto Rico and the USVI today, stay tuned for any updates.

- An increase in atmospheric instability is forecast this weekend and into the upcoming workweek, promoting a limited to elevated flooding risk. ESE steering flow to return by Sunday.

- A low risk of rip currents will persist through at least early Tuesday. However, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers.

Short Term(Today through Sunday)

Issued at 425 AM AST Fri Oct 9 2026

Fair conditions prevailed over the night hours with few passing showers moving mainly over the offshore waters. Since midnight, the radar estimated minimal accumulations over sectors of the USVI and eastern interior PR. Minimum temperatures ranged in the low 60s to low 70s across the interior and higher elevation regions of Puerto Rico. Whereas it ranged in the mid 70s to low 80s across the coastal regions of the islands.

This fair weather pattern is expected to continue throughout most of the day as a mass of drier air moves into the CWA. This will bring precipitable water (PWAT) values to below seasonal levels and dry low-to-mid levels (700-500 mb). This will act to limit the development of convection. A couple of mid-level high pressure systems are currently leading to warmer temperatures and weaker than average lapse rates at these levels further capping the potential for the development of deep convective cells. Thus the activity that does develop will be driven by local effects. A surface-induced trough currently located east of the US Virgin Islands and Puerto Rico is setting a breezy steering flow from the E. As the day progresses and the disturbance gradually approaches the islands to the northeast, the flow will shift to the ENE bringing drier and cooler air into the region. Model guidance suggest that these features will lead to showers and isolated t-storms with a focus over southwestern Puerto Rico during the afternoon. Streamers from El Yunque and the local islands may still develop and bring rainfall activity to the US Virgin Islands and eastern Puerto Rico during the afternoon hours. While the 925 mb temperatures are expected to be warmer than average the drier air can help limit heat indices, these conditions will lead to a limited heat risk for today. Nonetheless, places that are prone to excessive heat may experience brief periods of elevated heat risk. Individuals are invited to remain alert of the evolving weather conditions.

In contrast, for Saturday as the surface-induced through moves closer to the region and the mid-level high pressure systems moves further north, the mid-troposphere will tend to cool into the afternoon gradually acting to steepen the lapse rates at these levels by Sunday. This means that the potential for deep convective cells will increase into the remainder of the short term period. The PWAT and column relative humidity values will also increase favoring the development of showers and thunderstorms. The surface-induced disturbance will continue to promote a breezy ENE flow. These features combined with local effects will make Saturday the most active weather day of the short term period with convection expected to predominantly affect the interior and southwestern Puerto Rico during the afternoon. Similarly, rainfall from streamers in the afternoon and advective showers during the night and morning will affect the US Virgin Islands and northeastern Puerto Rico. Thus, a more widespread convective pattern is expected over the area on Saturday along with a limited heat risk.

By Sunday, PWAT and column relative humidity values are expected to decrease but remain near seasonal levels. While the surface-induced through will move further north, an upper-level low pressure system will move into the vicinity of the islands to the southeast and south acting to further cool mid-tropospheric temperatures and steepen lapse rates. In addition, an upper-level jet will lead to enhanced upper-level divergence and ventilation across the region. These features will aid in the development of deep convective cells. The wind flow will be breezy and shift to be from the ESE. Model guidance suggest that these conditions will favor a seasonal rainfall pattern, similar to Saturday but more localized. With a shift in the location of rainfall to be over southeastern and northwestern Puerto Rico. The heat risk for Sunday is forecast to be limited.

Long Term(Monday through Friday)

Issued at 425 AM AST Fri Oct 9 2026

A strong upper-level low will be the dominant feature throughout the period. Associated instability will drive 500 mb temperatures below 9 degrees Celsius on Monday and maintain values below -7 degrees Celsius through midweek, causing steep mid-level lapse rates. This setup, combined with seasonal PWAT values around 1.85 to 2.10 inches, daytime heating, and local effects, will support deep, organized convection each day. Furthermore, as the upper-level low tracks south of the islands, it will continue to deepen moisture through the atmospheric column.

On Monday and Tuesday, light-to-moderate easterly flow will steer slow-moving showers and thunderstorms, primarily focusing activity over the interior to western sections of Puerto Rico. For the remainder of the period, winds will shift more east-southeasterly and strengthen, shifting the convection to the interior and northwestern Puerto Rico. Regardless, passing showers and thunderstorm activity cannot be ruled out across eastern Puerto Rico and the USVI each day.

These conditions will maintain a risk of urban and small stream flooding, with flash flooding possibleparticularly on Monday, when lighter winds will favor slow-moving showers with higher rainfall accumulations. In addition, localized strong wind gusts and frequent lightning are expected with the strongest thunderstorms.

AVIATION

(06Z TAFS) Issued at 425 AM AST Fri Oct 9 2026

VFR conds expected for the terminals. Passing VCSH across eastern terminals during the morning. Between 09/17-22Z, SHRA/-TSRA are expected to develop across the interior into W PR, this can affect TJPS/TJBQ. Streamers can also affect the eastern terminals at this time. ESE winds to start the period will back to become more ENE during the afternoon. Winds increasing to around 15 kts with higher gusts and sea breeze variations after 09/13Z, decreasing after 09/23Z. VCSH/-SHRA reaching eastern terminals overnight.

MARINE

Issued at 425 AM AST Fri Oct 9 2026

Weak surface high pressure over the central Atlantic continues to drift eastward, displaced by a frontal boundary moving east across the western Atlantic. This is resulting in weak pressure gradient, maintaining mainly gentle to moderate easterly trade winds. Another surface high-pressure will build across the western Atlantic over the weekend, sustaining moderate to locally fresh easterly trade winds. An induced surface trough over the weekend could promote rounds of showers and thunderstorms across the local waters.

BEACH FORECAST

Issued at 425 AM AST Fri Oct 9 2026

The beach forecast remains on track. As mentioned in the previous discussion, beach conditions were expected to improved during the night hours into today, lowering the rip current risk. Although the risk is low, beachgoers should pay attention to the beach conditions as life-threatening rip current can occur in the vicinity of jetties, piers, reefs, and groins. In addition, beachgoers must remain weather alert, as shower and thunderstorm activity es expected each day, particularly near the western coastal areas of the islands. In addition of periods of heavy rainfall, thunderstorms can also bring gusty and frequent lightning. The low risk should remain low throughout the holiday weekend, becoming moderate by Tuesday into Wednesday.

FIRE WEATHER

Issued at 425 AM AST Fri Oct 9 2026

A low-to-moderate risk of fire danger will continue across the southwestern coastal plains of Puerto Rico (mainly during the morning) due to breezy winds and a drier air mass over the region. Winds are expected to begin from the east-southeast (ESE) in the morning and back to the east-northeast (ENE) during the afternoon. This shift to ENE flow could trigger showers and thunderstorm activity across southwestern Puerto Rico by the afternoon, helping to alleviate fire concerns. We will continue to track evolving weather patterns and fuel moisture levels for any potential increase in fire risk.

SJU WATCHES/WARNINGS/ADVISORIES

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