Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
331 FXCA62 TJSJ 031717 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 117 PM AST Tue Nov 3 2026 ...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 107 PM AST Tue Nov 3 2026 - Warmer and humid conditions continue today, particularly across urban and low-lying areas of the islands. Therefore, the Heat Advisory is now in effect through 4 PM AST. - For the rest of the afternoon, showers and isolated thunderstorms are expected across the interior, western, and northwestern Puerto Rico, leading to ponding of water over roadways and minor flooding. - A wetter pattern is expected from Thursday through Saturday. Increasing moisture and slow-moving showers and thunderstorms could raise the flooding threat, including urban and small- stream flooding, with isolated flash flooding possible. - Another swell is forecast to arrive this Friday into the weekend, bringing hazardous seas and life-threatening rip currents. Refer to the Beach Forecast section for additional details. && .Short Term(This evening through Thursday)... Issued at 107 PM AST Tue Nov 3 2026 Abundant low-level tropical moisture remains entrenched mainly across the Caribbean Sea, with precipitable water (PWAT) values just over 2.00 inches. However, recent upper air data show lingering mid- level dryness, keeping convective development somewhat localized today. With light south-southeasterly low-level steering flow below 10 knots, intense solar heating will interact with sea breeze convergence and local topography to trigger scattered afternoon showers and isolated thunderstorms mainly across the interior, western, and northwestern sections of Puerto Rico. Across the U.S. Virgin Islands and eastern Puerto Rico, isolated passing trade wind showers will produce minimal accumulations, allowing temperatures to rise into the upper 80s to low 90s, with heat indices increasing to near 108F. A heat advisory remains in effect until 4 PM this afternoon. By Wednesday, in response to a developing surface low pressure from a frontal boundary well north of the region, moisture content will gradually increase as winds shift more southerly, pulling the moist tropical air northward into the region. Aerosol models indicate a surge of minor concentrations of suspended Saharan dust filtering into the region, contributing to hazy skies. However, steady erosion of mid-level dry air and rising instability indices will favor more widespread convective initiation than today. PWAT will increase above climo, up to around 2.25 inches. Weak southeasterly steering winds will maintain primary convergence over the Cordillera Central and the northern and western slopes of Puerto Rico during the afternoon. Strong daytime insolation, steep low-level lapse rates, and favorable convective instability will support strong thunderstorm development capable of producing heavy rainfall, frequent lightning, and gusty winds. Consequently, the potential for urban and small-stream flooding will increase significantly due to the expected slow-moving showers. Thursday will be the most active day in the short term, as deep- layer moisture pooling and strong low-to mid-level moisture flux convergence overspread the region. Tropical moisture embedded in a deep southwesterly wind flow will support scattered showers and isolated thunderstorms across the regional waters and coastal areas of PR during the morning, followed by widespread, intense afternoon convection across the interior and northern and eastern quadrants of PR. With continued weak steering and persistent cell training, the threat of urban and small-stream flooding, localized flash flooding, and landslides in steep terrain will increase. && .Long Term(Friday through Tuesday)... Issued at 257 AM AST Tue Nov 3 2026 For Friday through Saturday, atmospheric instability is expected to remain elevated. Precipitable water (PWAT) values will continue above normal (between 2 to 2.3 inches) through at least Sunday. Relative humidity (RH) in the 850700 mb layer will stay high while mid-level moisture (700500 mb) is set to increase to 80% through early Saturday. An upper-level trough, along with its corresponding surface low and frontal boundary, will track northward across the Atlantic. Although the core of maximum instability is expected to pass north of the area, this will set up a southwesterly to westerly (light to variable) steering flow, drawing tropical moisture northward into our area. This steering flow will be generally light and variable. Consequently, slow-moving showers are likely to develop, generating elevated rainfall totals, primarily across the southern, interior, northern and northeastern sectors of Puerto Rico, as well as the U.S. Virgin Islands. This will result in flooding (Risk level 2 of 4) especially across interior, northern and northeastern Puerto Rico during the afternoon hours. Although model guidance continues to indicate mid to upper level ridging building over the islands to start the next week, prompting a more stable pattern. Model discrepancies continue through Tuesday. The GFS preserves higher moisture availability throughout the atmospheric column, specifically within PWAT, 850700 mb RH and 700- 500 mb RH. Conversely, the ECMWF projects a drier 850-500 RH profile alongside reduced PWAT values. Uncertainty continues to be present concerning the overall moisture content. While daytime heating and local effects can trigger isolated to scattered afternoon showers across the islands, an overall reduction in rainfall coverage and intensity is anticipated, thereby lowering the risk of flooding. Steering flow Sunday through Tuesday is forecast to be generally light to variable from the southwest before gradually backing and becoming more southerly as the period continues. Please monitor future updates as changes to the forecast are possible. && .AVIATION... (18Z TAFS) Issued at 107 PM AST Tue Nov 3 2026 Mainly VFR conditions are expected to prevail across all terminals through much of the forecast period. However, locally induced afternoon SHRA/TSRA over the interior and NW PR may cause tempo MVFR conds at TJBQ, while VCTS prevails at TJPS through 03/21Z. Mostly VCSH expected across the rest of the PR and USVI terminals. The 03/12z TJSJ sounding indicated variable winds up to 6 kt blo 2500ft. However, after 03/13z sfc winds acquired a SE component up to 12 kts, while a weak northerly sea breeze variations were observed along the northern coast of PR and should diminish by 03/21z. HZ due to suspended Saharan dust is expected through late Wednesday, but VSBY should remain P6SM. && .MARINE... Issued at 107 PM AST Tue Nov 3 2026 A surface high pressure in the Western Atlantic will continue to maintain light to moderate east to southeast winds for the rest of the afternoon and tonight. However, winds will gradually weaken and become light from the south-southwest as a surface low develops north of Puerto Rico and weakens the pressure gradient Wednesday onward. Seas will generally subside through Friday, though the arrival of a north-northwesterly swell arrives Friday into the weekend, building seas across the local Atlantic waters and Caribbean passages, creating locally hazardous conditions for small craft. Shower and thunderstorm activity is forecast to increase across the regional waters on Thursday and Friday, bringing gusty winds, slightly reduced visibility, and lightning. && .BEACH FORECAST... Issued at 107 PM AST Tue Nov 3 2026 The moderate risk of rip currents continues across northern and eastern-exposed beaches of Puerto Rico, including Culebra, and the U.S. Virgin Islands; low elsewhere. Beachgoers must exercise caution while visiting beaches under moderate risk, as life-threatening currents are possible along the surf zone. The risk should gradually lower tonight through Friday, as the steering wind flow weakens, though isolated rip currents could occur near jetties, piers, reefs, and groins; beachgoers should pay attention to the beach conditions. A high rip current risk is likely this weekend, as a north- northwesterly long-period swell generated by the low pressure developing well north of the region arrives by Friday. Based on the latest model guidance, the swell could increase breaking waves and lead to hazardous conditions for beachgoers, particularly on Saturday and Sunday, across north-exposed beaches of the islands. Residents and visitors should continue to monitor the beach conditions and stay up to date with the latest beach forecast. Aside from rip currents, beachgoers should also pay attention to the weather conditions, as showers and thunderstorms each afternoon could move near coastal areas of the islands, increasing the likelihood of lightning. Seek shelter whenever you hear thunder. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013. VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002. AM...None. && $$ SHORT TERM/AVIATION...DS LONG TERM....MRR MARINE/BEACH FORECAST...MNG