FXCA62 TJSJ 032035 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 435 PM AST Tue Dec 3 2024 .SYNOPSIS... A mix of sun and clouds, with passing showers is expected to prevail during the upcoming days. Showers will be stronger in the afternoon across northwestern Puerto Rico. Temperatures will remain warmer than normal, with highs mostly in the mid and upper 80s. A moderate rip current risk will persist for the north-facing beaches in Puerto Rico and the Virgin Islands. && .SHORT TERM...Tonight through Thursday... Mostly clear skies were observed across much of the interior and west during the morning hours, while a few brief passing showers affected eastern areas. Around noon, rainfall activity began to develop and moved swiftly across the region, affecting several municipalities in the east, west interior, and northwest Puerto Rico. Daytime maximum temperatures reached the mid to upper 80s across coastal areas, and climbed into the lower 90s in the south-central region. Temperatures were slightly cooler in the mountainous areas. Tonight, weather conditions will be influenced by the east- southeasterly wind flow, that will drag fragmented patches of clouds and showers. As a result, the islands can expect isolated moderate to strong showers as it has been the case in the past several days. However, significant rainfall accumulation is not anticipated. These showers will primarily affect the U.S. Virgin Islands and eastern sections of Puerto Rico, reaching as far inland as the vicinity of Caguas. From Wednesday into Thursday, similar weather conditions are expected to prevail due to the influence of a mid to upper-level ridge, which will maintain a stable atmosphere. Consequently, the islands will remain under the influence of shallow moisture driven by the east to east-southeast winds. In terms of temperatures, values at the 925 mb levels are still running slightly above normal, meaning that highs and lows above the climatological value will persist, especially along coastal, urban, and low-elevated areas. .LONG TERM...Friday through Tuesday.../from prev discussion/ A mid-high pressure building over the Caribbean will be the dominant weather feature from Friday to Sunday or Monday. This weather pattern will dry out the mid-levels and promote subsidence throughout the period, confining the available moisture around/below 850 MB. As the mid-level high pressure migrates into the western Caribbean, a TUTT-low will amplify from the northeast into the US Caribbean by late Monday into mid-next week. This TUTT-low will approach the islands from the northeast, inducing wind perturbations advected across PR/USVI by the trade winds, especially from Monday to Wednesday. The global model shows a discrepancy in the intensity and position of the TUTT-low, which, in the end, will impact the weather that develops across the local islands. Therefore, high uncertainty in the amount of precipitation we may see is present in the long-term forecast. The amount of low-level moisture pooling over the islands will be modulated by the interaction between a cold front exiting the US Eastern Seaboard (around the end of this workweek), the remnants of an old boundary, and the surface high-pressure building across the North Atlantic Ocean. At the moment, those frontal boundaries will not cross the islands. Still, the easterly or northeasterly winds will pool abundant low-level moisture across the northeast Caribbean, promoting a tropical winter advective rain pattern. In general, you can expect a mixture of sunshine and clouds each day, with pockets of moisture embedded in the winds arriving, especially in the morning and night hours. During the afternoon, the rain activity developing across western PR will be mainly due to orographic effects, diurnal heating, and sea breeze variations. The frequency and intensity of the rain activity will increase next week as the ridge pattern aloft weakens and trade winds- induced perturbations affect the region. With the return of the trade winds, we may observe a cooling trend in temperatures. However, the extent of this cooling is still correlated to the sea surface temperatures. Despite the cooling we could see compared to previous months, sea surface temperature anomalies remain one to two degrees Celsius above the normal values for this time of year. && .AVIATION... (18Z) VFR conditions will persist for most of the period across all TAF sites. Afternoon showers would result in MVFR conditions across some TAF with VIS reduction, TSRA, and lower ceilings in the FL020 & FL030. Winds will continue up to 15 knots from the E-SE, becoming more light at at around 04/00Z. && .MARINE... A surface high pressure over the central Atlantic and a frontal system extending across the western Atlantic will promote a moderate to locally fresh east to east-southerly wind flow through at least Wednesday. Winds will then return from the northeast as the frontal boundary lingers north of the northeastern Caribbean from Thursday onward. Confused seas due to locally induced seas and an easterly swell are expected around Thursday. A northerly to northwesterly swell could move across the Atlantic Offshore waters by the weekend. && .BEACH FORECAST... A small northerly swell continues to reach the local islands. This, along with the local winds, will maintain a moderate rip current risk for the north-facing beaches across the islands. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...ERG LONG TERM....CVB