Saturday, 3 March 2018

The "once-in -a-generaton storm" 5 years after Superstorm Sandy

U.S. Northeast Battered by Second ‘Once in a Generation’ Storm This Year

2 March, 2018

A major nor’easter is lashing the Eastern U.S. today. Reports of moderate to severe tidal flooding are racking up as hurricane force gusts are pushing mounds of water inland and raking the coastline with tremendously powerful waves.
This storm blew up to extreme intensity over the night-time and early morning hours on Friday as two low pressure cells converged off the U.S. coast. By afternoon, the storm had bombed out to 970 mb and was still intensifying.

A broad region across the northeast from D.C. to Maine are now experiencing wind gusts of 50 to 80 mph or more with local power outages and downed lines reported over a broad region. The gusts are so strong and widespread that diverse locations all throughout the Northeast are seeing instances of toppled trees, damage to structures and falling limbs. In Chambersburg, PA, the raging gusts tipped over a school bus.

On the coast, extremely strong winds for a nor’easter and conditions more akin to a hurricane are driving directly in to shore from Chatham and Nantucket northward. As a result, weather authorities are predicting a historic coastal flood event for metropolitan areas like Boston. There, record high tides may be exceeded as winds there are now blowing at a vicious 80 mph.



(A broadening storm is lashing most of the Northeastern U.S. with gale and hurricane force winds even as a places like Boston face massive waves and record storm surge flooding. Image source: Earth Nullschool.)

But what is, perhaps, more concerning is the fact that this storm is still gathering strength. And due to a blocking high over Greenland, the storm — dubbed Riley — is likely to only slowly move off-shore. So its impacts will tend to persist for multiple high tide cycles even as its circulation broadens and it generates an east-to-west fetch of gale to hurricane force winds stretching over a 400 to 600 mile region of ocean and driving directly toward the Northeast and East Coasts.
This will enable a long-lasting storm surge that will generate serious flooding for hundreds of miles of coastline. And on top of that surge, towering waves will relentlessly batter the coast throughout Friday and Saturday. Already the flooding has become quite severe for a number of locations. But the situation is likely to get worse before it gets better. With the worst impacts expected at high tide late tonight.

Scenes like these bring back recollections of Sandy. And like Sandy, the present cyclone has been influenced in a number of ways by human-caused climate change.

The storm’s historic intensity was first fed by a large plume of moisture issuing off a much warmer than normal Gulf of Mexico. Instability, driven by a deep diving trough, formed a low sweeping over the north-central U.S. that then tapped this high volume of moisture. The latent heat in the moisture enabled stronger than normal convection which helped to spike the storm’s early intensity.
(Extremely warm sea surface temperatures both in the Gulf of Mexico and off the U.S. East Coast are helping to fuel the present storm’s record intensity. This is just one of the climate change associated factors contributing to the present storm. Image source: Earth Nullschool.)

Off shore, the Gulf Stream waters are also far warmer than normal. Ranging as high as 9 degrees Celsius above average, this abnormal heat helped to fuel a second plume of moisture and instability. And as these two areas of storminess merged, they rapidly bombed out to high intensity even as their area of storm wind circulation broadened.
To the north, a recent (climate change driven) polar warming event has generated a kind of train wreck in the upper level winds that typically hurry storm systems along. As a result of this train wreck, a blocking high over Greenland is preventing this heat-amplified storm from tracking eastward. Over the next 48 hours, this block will allow a massive pile of water and towering waves to relentlessly hammer the Northeastern and Eastern Coasts of the U.S.
(Large waves and long fetch which is predicted to be generated by this storm on Saturday could produce serious and wide-ranging impacts all up and down the Eastern Seaboard from Hatteras to Portland and points northward. Image source: Earth Nullschool.)

Presently, this storm is expected to produce the second 1 in 100 year flood event that the Boston area has seen in the past year. Under typical climate variability, the likelihood of seeing back-to-back events of this kind would be 1 in 10,000. However, due to the influences of human-caused climate change, the potential for extreme weather events like the one we are presently enduring are greatly enhanced.

(UPDATES TO FOLLOW)


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