Weather with Bill Evans

National Weather Service New York NY Wednesday Dec. 11, 2024 *A Flood Watch is now in effect for southern CT from 1 pm this afternoon through 1 am Thursday. *A High Wind Warning remains in effect for Long Island, and southeastern CT. A Wind Advisory remains in effect for the NYC metro, Southern Westchester, and southwestern CT 1 pm this afternoon through 10 pm this evening. *Peak southerly winds 25 to 35 mph with gusts of 60 mph for Long Island and southeastern CT. Peak southerly winds 20 to 30 mph with gusts 45 to 50 mph in the Wind Advisory area. These winds likely occur in a 1 to 3 hour period this afternoon/early evening. Trees and power lines could blow down with possible power outages. *Widespread moderate to locally heavy rain into early this evening. A few thunderstorms possible, especially afternoon/evening when a line of low topped convection organizes and sweeps across from around the NYC metro on east. *Rainfall totals range from 2 to 3 inches. Locally higher amounts possible, especially across southern Connecticut and Long Island where 4 to 5 inches possible. Mainly minor urban and poor drainage flooding the main threat, but localized flash flooding possible. Some quickly responding rivers and streams could reach flood stage in southern Connecticut. Anomalous, deep upper trough will dig down to the Gulf Coast this morning, become negatively tilted this afternoon while pivoting towards the Middle Atlantic and northeast this evening. At the surface, a warm front will lift to the north this morning. A strong cold front will then approach into the afternoon with deepening low pressure passing from the Middle Atlantic into New England by this evening. The cold front should quickly race offshore tonight with the low moving into southeastern Canada. Rain will continue to overspread the area with the intensity picking up through the morning. Some embedded bands of heavy rain are possible as deep subtropical moisture is fed northward ahead of the trough and approaching frontal system. Moderate to locally heavy rain continues this afternoon, but there may be a brief min in coverage out east. There will also be a low topped convective line developing just ahead of the cold front this afternoon. The high-res CAMs have been consistent on this developing as far west as the interior of NE NJ and Lower Hudson Valley. The line will then quickly move east into the evening, but should become a bit more organized as it passes east of the NYC metro into S CT and Long Island due to the intense low level jet (75-85 kt). Once the convective line moves east, trailing stratiform rain will continue a few hours longer before the rain ends. Dry conditions are expected to prevail late this evening into the overnight. The 75-85 kt low level jet stream overspreading the coast in the afternoon and early evening, combined with only a weak low-level inversion, will present potential for damaging wind gusts across LI and SE CT, with wind advisory winds gusts for the remainder of the coastal plain, including NYC. BUFKIT analysis and HRRR wind gust potential continue supporting the ongoing high wind warning for LI, coastal New Haven, and Middlesex and New London counties for 55 to 60 mph gusts Gusts 45 to 50 mph look probable for the next tier of counties inland. Winds will shift to the W with cold frontal passage in the evening, and continue gusty with cold advection (25-35 mph) much of the night. Temperatures will reach unseasonably warm levels in the lower 60s, potentially middle 60s in NE NJ, this afternoon. Temperatures drop significantly behind the front tonight with lower to middle 30s likely by day break Thursday. Gusty winds and drying low levels overnight should allow any standing water to evaporate, limiting black ice potential where temps do drop below freezing inland. Strong cold advection follows the cold frontal passage on Thursday, with a secondary front moving through late in the day. The parent low pressure deepens as it tracks into Quebec, and surface high pressure begins to build in from the west. This tightened pressure gradient will keep a strengthened flow in place. The cold air aloft should allow mixing toward 850 mb, keeping conditions blustery through the day with westerly gusts 25 to 35 mph. With 850 mb temps progged around -11C to -13C, afternoon temperatures should only achieve the mid 30s inland to the lower 40s near the coast. The gusty conditions will make it feel like it is in the 20s. Conditions will remain dry under mostly sunny skies. Winds will begin to drop off Thursday night as the pressure gradient relaxes and high pressure moves towards the east coast. Lows will generally be in the low to mid 20s with some upper teens inland. The high pressure will strengthen as it settles over the northeast on Friday. Most of the models have the high pressure peaking around 1046-1048 mb over New England Friday night/Early Saturday morning. Dry and cold conditions will continue during this time with highs on Friday only in the 30s and nighttime temperatures in the upper teens inland and lower to middle 20s elsewhere. The strong 1046-1048 mb surface high passes just north of the local Tri- State into Saturday, and the flow veers around and becomes onshore by Sunday as the center slips into the Canadian Maritimes. This will help nudge temperature up from the 30s and 40s Saturday to the 40s and low 50s Sunday. Increasing low level moisture with the flow should lead to a good amount of lower clouds on Sunday as a weak mid level wave and warm front approach, though it remains unclear if the associated precip dissipates before reaching the area. Another frontal system may move through early next week, but guidance disagrees with timing and intensity. Kept PoPs capped at chance (50%) for now until the picture becomes clearer, but at this time the first few days of next week appear unsettled. Left precip at rain and/or snow at this stage, but more likely would be either all rain or perhaps a wintry mix well inland based on soundings and warmer air moving in aloft. Low pressure and its associated cold front will impact the waters into this evening. Southerly winds and ocean seas will quickly increase this morning, becoming Gales by midday. A strong low level jet moves across this afternoon and early evening brining a period of storm force winds on all waters except the NY Harbor. Rough seas are expected with this system, up to 4-7 ft on the Sound and 12-18 ft on the ocean late afternoon into tonight. Westerly gales are expected tonight in the wake of the system, mainly on the ocean and eastern Sound. Gales are likely to continue through Thursday afternoon, mainly on the ocean. Winds lower below 25 kt on all waters Thursday night and ocean seas gradually lower from over 10 ft Thursday morning, to under 5 ft by late Friday morning. Sub SCA conditions then persist on all waters Friday into the weekend. A widespread 2 to 3 inches of rainfall likely into this evening. Locally 4 to 5" amounts are possible across southern Connecticut and potentially up to 4 inches across portions of Long Island. Rainfall rates should mainly be one quarter to one half inch per hour, but heavier pockets of rain could reach around 1 inch per hour. 1 inch+ per hour rates appear more likely to occur in a narrow line of showers and embedded thunder this afternoon and early evening, especially across southern Connecticut and Long Island. The line will be quick moving which will limit the duration of the heavier rainfall and flood potential. However, headwater guidance indicating that around 3 inches/6hr or 4 inches/12hr would be sufficient for some quicker responding river/streams to reach minor flood stage. A Flood Watch is in effect this afternoon and evening across southern CT. Otherwise, the primary threat from this rainfall will be minor urban and poor drainage flooding. A localized occurrence of flash flooding cannot be ruled out. Water levels should remain below minor benchmarks with this mornings high tide. While peak surge is expected to occur this afternoon and early evening, water levels for most locations should once again remain below minor flooding benchmarks. But with a gradual windshift from southerly storm force to SW SCA just before or during the time of evening high tide, potential for areas along the southern bays of LI, south facing shoreline of twin forks, and coastal CT to see minor coastal impacts from combo of elevated water and splashover from wave action. This includes the eastern Great South Bay as water levels may remain elevated and could touch minor benchmarks as a strong southerly flow switches to the southwest, preventing water from escaping the bay quickly. The combination of 10-15 ft breakers during the evening high tide will cause widespread beach flooding and erosion. Scattered area of dune base erosion, and localized washovers possible for LI beaches where dunes protection is compromised.