Year: 2014

Heavy Rainfall and Flooding Recap 4/29-4/30

Miguel Pierre Uncategorized , , , , ,

Torrential downpours trained over the region late in the afternoon and overnight. Widespread rainfall totals between 4″ to 6″ fell along the I-95 corridor between the immediate New York City and Philadelphia metro areas. This caused moderate to major flooding in low-lying areas and along streams and rivers. A mudslide also buried two cars in Port Washington on Long Island.

DIXRadartotalrainfallCentral Park in New York also set a daily record rainfall record of 4.97″ for April 30th (storm total for two days is 5.12″). This was also the 10th wettest day recorded. Daily rainfall records were also set in LaGuardia Airport 5.26″ and JFK Airport 4.68, Newark Airport 5.24″.  LaGuardia and JFK had their 4th wettest days record. Newark had their 6th wettest day recorded.

An omega block this week caused a large cut-off low to from over the Central US.  “A cut-off low” is a storm that breaks away from jetstream and spins around very slowly, due weak steering currents. These lows sometimes bring prolific rainfall totals to our area. Especially during the spring or summer. So much moisture is transported from the Gulf of Mexico and the Atlantic and then is forced to rise and condense into very heavy rains.

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Heavy Rainfall & Minor Coastal Flooding Through Tonight

Miguel Pierre Spring Wx ,

As I discussed in the previous post, a large cut-off low that brought severe weather with tornadoes to our Central US is now bringing periods of rain to us.  Lifting and moisture will increase through the today as the warm front slowly approaches from the southwest. So more waves of rain, moderate to heavy at times mare expected for today. East winds gusting at times to 35mph will also keep us in very cool marine airmass. Temperatures will struggle to get out 40s. These winds will also cause some areas of minor coastal flooding during high tides this morning and early this afternoon. Especially along the shores of New Jersey and Western Long Island sound.

Tonight, a strengthening southerly low-level jet and an increasing precipitable water values will enhance moisture convergence for more widespread heavy rainfall. Elevated instability in form of MUCAPE will also be increasing for some embedded thunderstorms with torrential downpours. Rainfall totals between 2 to 4 inches are expected for most of the area. A few areas that receive more thunderstorms, could see higher totals.  This rainfall can cause flooding in the low-lying and poor drainage areas and flooding near small streams and rivers. Winds turning southeast early tonight, will cause more widespread minor coastal flooding during high tides. For these reasons, the National Weather Service have issued Flood Watches for the entire Tri-State area today and tonight. As well as Coastal Flood Advisories for areas around Western LI sound, New York Harbor for early tonight.

6z GFS showing heavy rainfall and embedded thunderstorms tonight over the region.
6z GFS showing heavy rainfall and embedded thunderstorms over the region tonight

Any rain and thunderstorms should come to end early tomorrow morning, as the warm front lifts north of the region. Some sunshine will break out between clouds later in morning and during the afternoon with winds turning more southwest. Causing temperatures to rise into lower to middle 70s, away from immediate coast. Which will be a big difference from what we are experiencing today. Some scattered showers and thunderstorms are possible late tomorrow afternoon with passage of a weak cold front. Friday still looks drier and slightly cooler, as the entire system weakens and lifts to our north.

I will have more updates on the storm, if there any significant changes. Check the 7-day Forecast and Forecast Summary for more updates later today.

Cut-Off Low to Bring Heavy Rainfall Midweek

Miguel Pierre Spring Wx

Hope you enjoyed today’s weather. A large, slow moving cut-off low will bring cooler and wetter beginning tomorrow. This is part of the same storm system that also causing severe weather with tornadoes to our West. Severe weather is not expected for the Tri-State area, due to onshore winds bring stable marine airmass over our area. But periods of rain likely to begin Tuesday afternoon and last into Wednesday. Then that rain will become steadier and heavier at times by Wednesday night. As a warm front approaches from southwest, with a 50kt+ low-level jet and precipitable water amounts 1.50″+. This will result in strong moisture convergence and elevated instability, enhancing heavy rainfall and isolated thunderstorms. Total rainfall totals from this storm are likely to range between 2 to 4 inches, for the most of the area. Some spots could receive more. Some flash flooding may occur in the typical poor-drainage areas. Some small stream or river flooding may also occur. Minor coastal flooding may also occur with easterly winds and astronomically high tides with the new moon. Especially for areas around New York Harbor and Western Long Island sound, Wednesday night.

12z GFS showing strong low-level jet at 850mb (5000ft)
12z GFS showing strong low-level jet at 850mb (5000ft)
12z GFS showing precipitable water values at 1.50 inches and higher, Wednesday night.
12z GFS showing precipitable water amounts of 1.50 inches and higher, Wednesday night.

The cut-off low will gradually weaken and move north of the area late this week. The warm front is forecast to lift well north of the area on Thursday. Some sunshine will break out between clouds, causing temperatures to rise into the 70s away from immediate coast. However, this may also cause more instability, for more scattered showers and thunderstorm to develop with an approaching cold front in afternoon and evening hours. Friday is looking cooler but drier. More disturbances coming from the northwest may bring scattered showers and thunderstorms this weekend and early next week. But there will be some sunshine as well.