Unprecedented all time record rain swamps Long Island

If the Discovery Channel aired "Extreme Flood Week" this would be it.

Monday was Detroit. The city recorded the 2nd wettest day of all time. On Tuesday, Washington D.C and Baltimore did the same.

New York's Long Island became the 3rd major metro area drenched by extreme, even unprecedented rainfall this week. Islip, New York set the all-time 24-hour state record rainfall today with an incredible 13.26 inch deluge.

The extreme torrential downpour produced rainfall totals up to 5 inches per hour early this morning, and spawned instant flash floods inundating freeways on Long Island.

An incredible 11 inches fell in just about 3 hours this morning. The staggering rainfall totals of 13"+ represent an entire summer's worth of rain, in just a few hours. Mashable's Andrew Freedman put the deluge in perspective:

The same unusually strong August storm system that brought five to eight inches of rain to the Detroit area on Monday night, paralyzing travel and flooding homes and businesses, dumped an entire summer's worth of rainfall on one Long Island town in just a few hours on Tuesday night and Wednesday morning.

In the New York City metro area early Wednesday, more than a foot of rain fell in just a few hours, causing extensive flooding on Long Island. As of 10 a.m. ET, Islip, New York had received 13.27 inches of rain, which set a preliminary state record for the heaviest 24-hour rainfall total in state history. This broke the previous record of 11.6 inches, set at Tannersville, New York in August of 2011 during Hurricane Irene.

The pace of the rain was extreme, as Islip picked up 5.34 inches of rain between 5 and 6 a.m. ET, and another 4.37 inches in the following hour.

Unprecedented storm

I can't recall a time when the same storm produced major flooding in 3 major urban areas in 3 days. I've talked and written about our stalled jet stream patterns this week, and how the coasts have seen weather extremes even as Minnesota has basked in pleasant San Diego-like weather.

So what happened?

Basically a slow moving upper level low pressure system slogged along the eastern half of the US this week. The system was deep enough to pull an unusually deep moisture plume from the tropical Atlantic.

The University of Wisconsin's CIMMS satellite blog has some excellent posts on the evolution of the moisture plume which led to the multi-day, multi-city flash flood event.

The system that caused flooding in Detroit, MI on 11 August and in Baltimore/Washington on 12 August has moved eastward: Islip, NY, on central Long Island, had historically heavy rainfall early in the morning on 13 August as more than 13″ of rain fell (10″ in two hours!!), smashing the New York state record for 24-hour rainfall (Record Event Report).

Very heavy rain has fallen during the day on August 12th in and around Baltimore (with rainfall rates as high as 2.70″ per hour at KBWI) and Washington DC, with reports of up to 10″. Where has this moisture come from? There are a variety of products available to diagnose total precipitable water in the atmosphere. The animation above, taken from the MIMIC Total Precipitable Water page (link), shows an influx of tropical moisture from the south-southeast has surged northward up to the east coast of Maryland on August 12. A mesoanalysis from SPC also suggests a link to the moisture east and south of Cape Hatteras. The GOES Sounder Total Precipitable Water derived product image at 1800 UTC, below, (from this website) showed very high total precipitable water amounts just south of Baltimore and Washington DC with values exceeding 60 mm or 2.4″. Soundings at 1200 UTC also showed high values of precipitable water: 48.5 mm or 1.90″ at Wallops Island, VA, and 44.7 mm or 1.76″ at Washington Dulles. 

Climate change in action?

There's no doubt that these type of extreme rainfall events are increasing in the eastern half of the US.

This well documented trend fits perfectly into the overall climate change picture. There will likely be much discussion in the coming days regarding the ability to attribute these individual record flash flood events, and the broader weather pattern this week to climate change.

These extreme rainfall events continue to increase in frequency as predicted by climate change theory. The case for attributing the "juicing" of individual flash flood events to the increase in atmospheric water vapor and stalled jet streams gets stronger with each record shattering deluge.