Forecast Highlights: A weak upper level trough continues to slowly progress east through the region, resulting in mostly cloudy skies through Friday along with a risk of locally heavy showers this evening, mainly west and …
Forecast Highlights: Mostly sunny skies and seasonable temperatures continued for another day as a high pressure slowly progressed further east. In its wake, more widespread cloud cover is expected tonight through Friday with a risk …
Forecast Highlights: Seasonable temperatures will continue into Tuesday, with mostly sunny skies expected to return for another day. An approaching trough may trigger scattered showers on Thursday, but with dry conditions otherwise likely to continue. …
Mostly sunny skies and seasonable temperatures continued for another day as a high pressure slowly progressed further east. In its wake, more widespread cloud cover is expected tonight through Friday with a risk of scattered showers on Thursday, but with temperatures gradually cooling down into the mid to upper 70s by the weekend as an easterly flow sets up with a cooler air mass aloft (image credit: NCEP MAG, 4k-NAM depicting scattered showers on Thursday night).
Seasonable temperatures will continue into Tuesday, with mostly sunny skies expected to return for another day. An approaching trough may trigger scattered showers on Thursday, but with dry conditions otherwise likely to continue. Meanwhile, a hot and humid air mass will build northward in the central US, with widespread high temperatures in the 90s and some 100s anticipated, but will be blocked from reaching the area by a stationary upper level low keeping temperatures near to below average (image credit: NCEP MAG).
With the end of meteorological summer half a month away, the upper level pattern remains unfavorable for any heat signal beyond 1-2 days across the region. Lower upper level heights persist over the region, likely to maintain near to below average temperatures through the next 7-10 days as a cool air mass persists through Monday before an onshore flow develops with more widespread cloud cover and a risk of rain later in the week (image credit: PSU e-Wall).
Forecast and Analysis Highlights:
A low pressure system affected the region with heavy rainfall last night, primarily centered over Long Island where excessive rainfall amounts of as much as 10-14 inches of rain were observed in a short period of time, leading to widespread flash flooding. Today’s post is mostly focused on analyzing the rainfall event from last night, along with a forecast update on the upcoming week and the next risk of rainfall (image credit: PSU e-Wall).
9:40 AM: Excessive Rainfall in Long Island
Last night’s rain event unfolded quite differently than what was originally expected. The heaviest rainfall was originally expected to fall in the western half of the area, but which ended up with some of the lowest totals with rain totals ranging from 1/2 inch in northeast NJ to slightly more than a trace in West Passaic county.
The heaviest rainfall was observed in Long Island, however, and significantly exceeded expectations. This system had a history of producing excessive rain totals, with over 6 inches falling yesterday in Baltimore and southern New Jersey. Training of heavy thunderstorms set up over portions of west-central Suffolk county early this morning, resulting in as much as 10-15 inches of rain in a short period of time. Islip, NY reported an excessive 13.10 inch storm total last night, including 12.92″ in 6 hours, and 9.71″ reported in only 2 hours. These locations remain under a Flash Flood Warning by the National Weather Service, set to expire later this morning.
Based on a quick analysis, the previous 1-day rainfall record in Islip, NY was 6.74″ on August 24, 1990, which was shattered by nearly twice as much rainfall last night. The previous monthly rainfall record was 14.07″ in September 2005, which last night alone fell only an inch short of breaking.
A more detailed analysis on last night’s event will be posted later this afternoon.
5:40 PM: Additional Rain in Parts of NJ, Long Island
Following last night’s heavy rainfall, the low pressure has tracked into Connecticut with the cold front moving through Long Island, although another area of showers on the backside of this system just ahead of the upper level trough developed over northeast Pennsylvania and continue to progress southeast through the area.
The main area of rain is over Bergen county, and will continue to progress ESE into southern Westchester, Bronx and northern Manhattan, northern Queens and northern Nassau through 6:30pm. With the moist air mass and anomalously high precipitable water values which aided in the excessive rainfall in Long Island last night having shifted offshore, these showers are producing less significant rainfall, generally around 1/4 to locally 1/2 inch. These scattered showers may persist into parts of Long Island before weakening or dissipating towards 7-9pm.
A full blog update with more information on this morning’s rainfall is currently in progress and will be posted tonight. A more thorough storm archive regarding this event is scheduled to be completed by next week.
Following a stretch of generally seasonable and sunny conditions, an approaching low pressure system will bring increased cloud cover and heavy rain for Tuesday and Wednesday, with upwards of 2 inches of rain expected north of New York City. A cooler and drier ending to the week is expected, but with a gradual warming trend towards the following week with indications signaling the possibility of 90s returning (image credit: NCEP MAG, 4k-NAM simulated reflectivity).
Calm weather conditions continue across the region as a high pressure remains stationed through Monday, providing the area with mostly sunny skies and temperatures in the mid to upper 80s. A deepening low pressure is expected to pass near the area on Wednesday, producing a period of rain and possible thunder, possibly heavy, while also pulling a colder air mass into the area for the late week with high temperatures only in the mid to upper 70s (image credit: PSU e-Wall).
NYC Area Weather is dedicated to providing objective analyses of the weather and quality-based forecasts, and work is currently in progress for new features to be eventually added into the website over the next year. In the short term, forecasting updates will be posted more frequently but may not be on a daily basis.
A poll has been opened to the right about a proposed post formatting change. The current posting format consists of a brief highlight section, followed by a more in-depth technical discussion. The proposed revision would feature a static homepage with a general forecast highlighting the sensible weather impacts, with a link to the technical discussion analyzing the reasoning behind the forecast, confidence level in the outlook and any margin of error. This would also allow short updates to be posted more frequently ahead of major weather events, as technical discussions are only posted once a day.
Below is a sample view of the proposed change: