Weather with Bill Evans

Good Day On This Wednesday October 4, 2023 High pressure over the region through Thursday will slowly weaken beginning Thursday night, and give way to an approaching frontal system on Friday. The associated cold front will pass through Saturday into Saturday night. Low pressure will then linger to the north as high pressure slowly build from the south and west. The warmest day of the current spell expected as high pressure at the sfc and aloft both strengthen. Another clear night expected tonight, with light onshore flow and development of river valley fog as has been the case the last few nights. Low temps should range from 60-65 invof NYC to the 50s elsewhere. & One last mostly sunny/warm day expected, though not as warm as Wed as the vertically stacked high begins to slide east out into the Atlantic. High temps should still reach the lower 80s in NE NJ, with mid/upper 70s elsewhere. Second night of onshore flow may lead to more widespread fog development Thu night. As the sfc ridge axis lifts to the north, sct to numerous warm advection showers should start to develop late Thu night offshore and spread to Long Island late Thu night, then to the rest of the area daytime Fri. Low temps again in the lower 60s in NYC and 50s elsewhere should warm up to the lower/mid 70s in most places on Fri, perhaps to the upper 70s in NE NJ. At the start of the long term period, the orientation of surface high pressure well to our north and east will continue the already prolonged period of SE-E onshore flow. This will advect an increasingly humid air mass into the area. In the meantime, an upper level trough approaches from the west as Tropical Storm Phillipe approaches from the south and east. The upper level trough will eventually become negatively tilted before closing off. At the surface, an associated cold front will swing through the area. There is much more interaction near our area with the upper level trough/surface cold front and Phillipe than was shown in the guidance 24+ hours ago. The original thinking was that a wave of low pressure would form over or near the area along the the cold front. It now looks like the negatively tilted trough may bend Phillipe back to the north and west well north of our area. The exact details will need to be fine tuned over the next several days. Regardless, a good 1-1.5 inches of rainfall is possible through Saturday, with the potential for periods of moderate to heavy rain. Both the NAM and GFS show PW increasing to 1.5-1.75 inches ahead of the cold front early Saturday. This has lowered slightly compared to 24 and 48 hours ago. NBM probabilities for 1 inch of rain over the 24 hr period ending 00Z Sunday have increased slightly after holding steady for the past two days. It now has a 35-45% chance over the northern half of the area and 25-35% across the southern half. See the Hydrology section below for more details on expected impacts. Rain chances taper off early Sunday and a cool air mass is advected in behind the cold front. The closed upper level low, as well as the surface low, remain over the northeast through the end of the forecast period. This will lead to a period of well below normal temperatures. The coolest days will be Sunday and Monday. Highs will be in the mid 50s to lower 60s, with lows in the 40s. After an extended quiet period with high pressure in control and a 2-3 ft SE swell, ocean seas will be building Fri night, and should reach 5 ft by Sat morning. A cold front will move through late Saturday and could bring gusts 25-30 kt to all waters from Sunday through early Mon. Ocean seas will remain elevated into early next week as long period swells from distant Tropical Storm Philippe move into the waters. Refer to the National Hurricane Center, https:/www.nhc.noaa.gov for official forecasts on Philippe. A period of showers is likely late Friday through late Saturday, with about 1-1.5 inches of rainfall expected at this time. The WPC now has southern CT and portions of the Lower Hudson Valley in a Day 4 marginal risk of excessive rainfall. The main threat in the marginal area is minor nuisance flooding, with the potential for isolated flash flooding.