Weather with Bill Evans

National Weather Service New York NY 508 AM EDT Mon Sep 16 2024 High pressure remains in control through Monday night, before gradually retreating north Tuesday into Tuesday night. A frontal system slowly approaches from the southwest through mid- week as high pressure drifts east in the northern Atlantic. Low pressure may linger nearby Thursday along a cold front. A back door cold front moves across Friday. High pressure from SE Canada builds in for the weekend. With deep layered ridging aloft and a large dome of high pressure at the surface, expect the dry weather to continue with mainly sunny to partly cloudy skies. The winds once again will be light and variable to begin the day, but with solar insolation, the winds towards late morning and mid day will become more ENE at around 5 to 10 mph. Temperatures at seasonable levels for mid September. For Monday night the upper level ridging begins to slowly break down. More in the way of high clouds attempts to work in as low pressure off the southeastern US coast begins to work NW. Partly cloudy to mostly cloudy skies are expected Monday night with a light E to NE flow remaining in place. With a bit more moisture in the lower levels there should be a reasonable chance to see some low stratus / patchy fog in many of the lower lying rural locations like previous nights as of late. Temperatures should average close to normal in outlying areas, and a bit above normal in the more urban areas. Surface high pressure will gradually begin to wane in strength on Tuesday. A southerly component to the flow aloft begins to get established during the afternoon as the region gets on the outer edge of the northeast quadrant of a closed low getting into the Lower Appalachians. The mid levels may moisten up enough to produce more in the way of mid level clouds, especially as the day progress. Thus a partly cloudy to mostly cloudy day from NE to SW across the region appears most likely. With more mid and upper level clouds compared to lower level clouds, expect the clouds to mainly filter out varying amounts of sun. Temperatures will once again run right around seasonable levels. Dew point readings should edge up in the 60s, especially along the coast as the day proceeds. The high slowly drifts east through mid-week. At the same time, low pressure over the Carolinas will slowly trek northwestward toward the Ohio Valley through mid-week. The associated frontal system will approach from the southwest and will begin to impact the region Tuesday night. The low and frontal system get caught under the upper level ridging over the eastern US from mid to late week and a prolonged period of some unsettled weather is possible as weak flow under the ridge will mean slow movement of these features. Right now, it looks like the most likely period of rain is overnight or early Wednesday morning through Wednesday night. There is a deep moisture feed from the tropics and training possible. Dew points rise well into the 60s Wednesday into Thursday and PWATs around 2" are seen in most of the guidance. Of course, this is all dependent on certain mesoscale features that cannot be resolved at this point, but there is a low chance right now of flooding, and the Weather Prediction Center has placed the entire forecast area in a marginal risk of excessive rainfall Wednesday into Thursday. With the previously mentioned uncertainty, stuck close to the NBM and did not go any higher than chance POPs through the long term. However, models have trended a little slower on the systems arrival, so have kept Chance POPs out of the forecast until 2am early Wednesday. At the surface, low pressure may still be not too far away to the south of Long Island Thursday into Thursday night. Chances for showers will remain in the forecast. A back door cold front moves across Friday, keeping shower chances in the forecast. However POPs are more in slight chance range since moisture becomes more limited as low to the south weakens and moves farther away. For Friday night into the weekend, dry conditions return as high pressure builds in from the north. Clouds may very well linger around to start but will be on a decreasing trend. Ocean seas may reach 4 to 5 ft by towards Tuesday morning into evening, especially for the western ocean. 5 ft waves are expected Tuesday night on the ocean waters. A SCA has been issued through 00Z Wednesday. More widespread 5 ft waves on the ocean waters are expected Wednesday on a persistent easterly flow. SCA conditions are forecast on the ocean Thursday through Friday night. Non-ocean waters initially remain below SCA thresholds Thursday and Thursday night, but their wind gusts are forecast to reach SCA levels for some portions at times Friday into Friday night. There will be a persistent pressure gradient with low pressure to the south of the region and high pressure to the north of the region to maintain a gusty NE flow.+ No hydrologic through the forecast period. An extended period of rain is possible from Tuesday night through Wednesday night with a tropical feed and training possible. There is still some uncertainty with regards to the amount of rain we may see. The Weather Prediction Center has placed the southern portion of the area under a marginal risk for excessive rainfall on Wednesday. One factor against flooding would be the antecedent dry conditions over the last week. With an approaching full moon on the 17^th, astronomical high tides will be rising into the first half of the week, with water levels potentially rising through the week. Continuous easterly flow will help build seas and allow for some piling of water. Winds are expected to remain generally light, near 10 kt or less. While some of the guidance is showing water levels increasing, there is a general consensus of keeping them below minor coastal flooding benchmarks for the most part, although Stevens suggest minor benchmarks being reached for the south shore bays and for western LI Sound locations towards late Tue / Wed. However, this will likely depend on the development of low pressure off the Carolina coast and its eventual track early next week. There is a moderate risk of rip current development at the ocean beaches Monday with an easterly flow developing, becoming high risk on Tuesday.