000 FXCA62 TJSJ 240830 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 430 AM AST Sun Jan 24 2021 .SYNOPSIS...Fair and stable weather conditions with limited shower activity are expected through early next week. The remnants of a weak cold front are forecast to linger across the region Tuesday through Thursday, merging with the remnants of yet another, but stronger frontal boundary by the end of the workweek into the upcoming weekend, supporting a higher chance for showers. Winds will remain light to moderate from the east to northeast through Monday, increasing thereafter. Tranquil marine conditions along with a moderate risk of rip currents will continue today. && .SHORT TERM...Today through Tuesday... There is a weak area of high pressure at the surface north of the local islands, which is causing light to moderate northeasterly winds across the local area. For Monday and Tuesday, a stronger SFC high pressure will be present across the southwestern Atlantic, causing stronger northeasterly winds across the local islands. Stable conditions are currently observed as a ridge dominated the mid and upper levels. According to the latest forecast soundings, near to below normal moisture are still expected over the local area for the next few days, with the limited moisture available mainly being in the lower levels. This combination of patterns is causing mainly fair weather over Puerto Rico and the USVI, with only isolated light showers occurring over the local waters during the night and early morning hours. However, for today, the hi-res models seem to be much more bullish in the rainfall forecast compared to the global models, mainly due to the local effects and diurnal heating over Puerto Rico. The NMM model was so bullish in the afternoon rainfall over W-SW PR, that it was difficult to ignore and thus scattered showers are in the forecast across central to the southwestern quadrant of PR for this afternoon. The other hi-res model, the ARW agrees with the NMM on the location of rain, but it has less amount of rain in the solution. As winds become stronger on Monday, the shower activity is expected to be mainly isolated and brief through the day. There is only a slight chance of rain on Monday afternoon, as the stronger NE winds should reduce the chances of sea breeze convergence over the SW portions of PR. Isolated and brief showers are forecast elsewhere in the local area through the day on Monday. However, on Tuesday, the remnants of a frontal boundary will be approaching the local area. Cloudiness and rainfall as well as available moisture is expected to increase. That said, the area with higher moisture and rainfall is limited to a narrow band, which will move through the local area during the day on Tuesday. At this time, it looks like there will be an increase in shower activity, but the rainfall accumulations are not looking like it would cause hazardous conditions more than some ponding of water in poor drainage areas. The daytime temps are expected to be near normal for the next few days, with the lower elevations observing daytime temps in the low to mid 80s and lows in the upper 60s to low 70s; while the higher elevations will have high temps in the mid 70s to low 80s, and overnight lows in the upper 50s to mid 60s. .LONG TERM...Wednesday through Sunday... Model guidance continues to suggest that a relatively moist weather pattern will dominate, particularly by the end of the workweek into the weekend. A surface high pressure streaming across the western Atlantic will push the remnants of an old frontal boundary southward across the local islands into the northeastern Caribbean on Wednesday into Thursday, promoting periods of increased cloudiness and isolated to scattered shower activity from time-to-time. As the aforementioned high moves away into the north central Atlantic and a frontal boundary approaches the region from the northwest, winds are to decrease and turn from the east to southeast, trapping an area of near normal moisture over the local islands through Friday. Further increase in moisture is expected thereafter as the remnants of the aforementioned frontal boundary move in along with the weakening of the trade wind cap that results from the passage of a deep polar trough. The combination of favorable conditions aloft with above normal moisture, with model-estimated PW values ranging from 1.5 inches on Friday morning to around 1.8 inches by Saturday night, will support enhanced cloud coverage and prolonged shower activity across the forecast area. Although it is too soon to determine potential impacts, if this forecast materializes, we could have the first rain event of the year. && .AVIATION...VFR conditions expected across the local terminals for the next 24 hours. Brief ISOL -SHRA is possible over the local flying area this morning, which could cause light and brief VCSH. VCSH possible at TJPS after 24/18Z as SCT SHRA develop over portions of south and west PR. Light and VRB winds will be observed until around 24/12Z, but NE winds and sea breeze variations at around 10 KT are expected thereafter until around 24/22Z. FEW to SCT SKY expected today. && .MARINE...Tranquil marine conditions with seas up to 5 feet are expected today, turning choppy up to 6 feet for the outer Atlantic waters tonight into Monday. Thereafter, another swell is expected to invade the regional waters, generating choppy to hazardous seas that may require the issuance of Small Craft Advisories. Winds will remain light to moderate from the east to northeast through Monday, increasing to 10-20 knots by Monday night. There is a moderate risk of rip currents for beaches along the north coast of Puerto Rico, all beaches in Culebra, eastern beaches of Vieques, north beaches of San Thomas and northwestern beaches of Saint Croix. && .FIRE WEATHER...Drier air will continue to move into the region, limiting any chance for wetting rains and causing relative humidity to drop into the mid 40s to near 50 percent, while promoting further deterioration of soils and fuel moisture across the southern coastal plains of Puerto Rico. Although winds are expected to remain generally light, sea breeze variations will cause winds to peak around 15 mph between the late morning and early afternoon hours. Both KBDI and 10-Hour Fuel Moisture values at Camp Santiago have reached already elevated thresholds during the previous day with 558 and 8 percent, respectively. Based in the expected weather conditions and recent drying pattern, a Fire Danger Statement has been issued for elevated fire danger conditions expected across the southern coastal plains of Puerto Rico today. && .PRELIMINARY POINT TEMPS/POPS... SJU 83 73 83 73 / 10 20 20 30 STT 83 73 83 72 / 10 20 30 10 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...JA LONG TERM....ICP PUBLIC DESK...ICP