Area Forecast Discussion (AFD)
916 FXCA62 TJSJ 290549 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 149 AM AST Tue Sep 29 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 133 AM AST Tue Sep 29 2026 - Limited heat risk for the next few days, as easterly trade winds strengthen, allowing only localized areas across Puerto Rico and the US Virgin Islands to experience brief periods near heat advisory criteria. - The US Virgin Islands and Puerto Rico should experience clear skies through the first half of the day, followed by showers and thunderstorms during the afternoon hours each day. Therefore, a limited flooding risk should prevail over western PR, increasing to elevated by the end of the workweek. - Moderate rip current risk for western, northern, and eastern PR, as well as, the US Virgin Islands, while the rest should experience low risk. Regardless, people are urge to exercise caution and always swim near a lifeguard. && .Short Term(Today through Thursday)... Issued at 133 AM AST Tue Sep 29 2026 Like previous nights, generally calm weather conditions prevailed across the islands, with only a few passing showers over the waters. Mostly clear skies allowed temperatures to fall into the 70s across urban and coastal areas, while observations across the higher elevations dropped into the upper 60s to low 70s. Winds remained light and variable. Overall, slightly drier conditions are expected through much of the short-term period as surface to mid-level high pressure remains the primary feature across the region, despite a weak upper-level trough lingering nearby. Limited moisture and weak forcing should keep precipitation chances relatively low through Wednesday. Current satellite imagery shows mostly clear skies across the islands, with only a few pockets of showers over the waters and occasionally moving into eastern Puerto Rico and the U.S. Virgin Islands. Generally sunny to partly cloudy skies are expected, along with gradually increasing winds through midweek. This pattern should provide favorable conditions for outdoor work and recreational activities, particularly during the morning and early afternoon hours. However, diurnal heating and local effects should still promote typical afternoon convection across western Puerto Rico, where a limited flooding risk will persist each afternoon. Regarding heat, a break from heat products is anticipated, as only localized areas are expected to briefly experience heat indices near advisory criteria. Nevertheless, those spending extended periods outdoors should continue to stay hydrated and take appropriate breaks, especially during the warmest part of the day. Conditions will begin to transition late Thursday as an upper- level trough and surface disturbance approach the region, allowing moisture to gradually increase. The first half of Thursday should remain generally favorable for outdoor activities, with increasing cloud cover and shower activity becoming more likely later in the day as moisture increases. This will mark the beginning of a slightly wetter pattern extending beyond the short-term period. Those with plans late Thursday and beyond should continue to monitor forecast updates as the potential for showers and associated impacts increases. && .Long Term(Friday through Tuesday)... Issued at 133 AM AST Tue Sep 29 2026 Unstable conditions are still expected on Friday and Saturday, transitioning to a typical weather pattern Sunday onward. Model guidance continues to suggest a surface high pressure the western Atlantic, promoting an E-SE wind flow throughout the period. As mentioned in the previous discussion, a surface trough may weaken the surface high, with isolated breezy conditions across coastal areas of the islands. Friday and Saturday remain the active days of the long-term, as the latest model guidance suggests that the presence of upper-level troughs should introduce instability across the eastern Caribbean. In terms of moisture, the deterministic guidance of the GFS and ECMWF continues to suggest abundant tropical moisture across the region, with PWAT values between 1.8 and 2.0 inches, mainly in the low and mid levels. Additionally, model sounding plots continue to show skinny profiles, with weak inversion caps that could easily be broken and high CAPEs. Due to the proximity of the troughs, mid-levels might get cooler than expected (500 mb temperatures reaching -8 C) with steeper lapse rates in the mid-levels, allowing cloud growth and instability aloft. Therefore, the most likely scenario should be for isolated to scattered showers across the windward sections during the night and morning hours, with deep convection in the afternoon, particularly across the interior and western/northwestern. Additionally, local island streamers are also expected, affecting the San Juan Metro Area. On Sunday, drier air is expected to filter in the low-to-mid-levels (850 - 500mb), inhibiting deeper convection over the islands, as precipitable water (PWAT) values are expected to drop to seasonal or below-seasonal values. However, local effects and daytime heating driven by an easterly flow should promote afternoon convection mainly over the interior to western half of Puerto Rico. A similar pattern is expected on Monday, as drier air persists in the low-to- mid levels. In general, shower and thunderstorm activity is expected each day, with the highest flooding threat on Friday and Saturday. Rainfall accumulations could enhance the chance of urban and small stream flooding over the aforementioned areas. Meanwhile, Sunday and Monday rainfall activity may lead to ponding of water over roadways and poorly drained areas, including minor flooding. In addition to flooding, thunderstorm activity could produce gusty winds and frequent lightning, without ruling out small hail. Warmer conditions are expected throughout the long term, with seasonal to above-seasonal 925-mb temperatures. Although heat indices should exceed 100 F, a limited risk of excessive heat will persist throughout the forecast period. Individuals sensitive to these conditions should stay hydrated and avoid prolonged outdoor activities. && .AVIATION... (06Z TAFS) Issued at 133 AM AST Tue Sep 29 2026 VFR conditions will prevail across all terminals. However, passing SHRA and VCTS may cause tempo and brief MVFR conds at TJPS/TJBQ from 29/17Z thru 29/21z. Elsewhere, mostly VCSH expected. Increasing winds from the ENE at 12-16 kt with higher gusts aft 29/13z. && .MARINE... Issued at 133 AM AST Tue Sep 29 2026 A small northerly swell will continue to gradually subside today while moderate easterly trade winds persist. Choppy conditions are expected across the Atlantic waters and Mona Passage, with winds strengthening tonight into Wednesday and becoming locally fresh. Seas will generally range from 3 to 5 feet, occasionally up to 6 feet across the Atlantic waters and passages. Periods of showers will continue, with afternoon showers and isolated thunderstorms developing mainly near western and northern Puerto Rico. Thunderstorms may produce locally higher winds and seas, lightning, and reduced visibility. && .BEACH FORECAST... Issued at 133 AM AST Tue Sep 29 2026 Beach conditions will improve today as the northerly swell gradually subsides. However, a moderate risk of rip currents will persist along the exposed beaches of northern and eastern Puerto Rico, as well as Culebra and the U.S. Virgin Islands. Breaking waves of around 5 feet are expected along portions of the northern coastline, with lower heights elsewhere. Afternoon showers and isolated thunderstorms may also pose a lightning threat to beachgoers, particularly across western and northern Puerto Rico. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM/AVIATION...MMC LONG TERM...MNG/JCP MARINE/BEACH FORECAST...ICP
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