Why strong winds, heavy rain may pummel New York on Sandy anniversary


(CNN) – Sunday marks the five-year anniversary of when Superstorm Sandy hit New Jersey and New York. This Sunday night into Monday morning, some forecast models show, another big storm will lash the Northeast.

This forecast banks off a tropical wave down in Central America, a low-pressure system swinging a cold front across the eastern US and a large dip in the jet stream — which is due to former Typhoon Lan now off the coast of Alaska — all merging at the same time near the Northeast coast. The magnitude of impacts depends on whether the weather all lines up.
If these systems do all merge (and it’s a big if), you may hear people begin to reference the “perfect storm” — a term used by meteorologists when everything in the atmosphere comes together just right for a storm to have dangerous conditions.
 Tropical storm-force winds, coastal erosion and flooding rains could then be possible from the mid-Atlantic through New England. One thing is for certain; this storm system is not forecast to be as strong as Sandy.
Currently, the National Hurricane Center is giving the tropical wave off the coast of Central America a 40% of tropical development over the next five days. The key word in this is the word “tropical.” We don’t expect that this storm will be tropical when it reaches the Northeast on Sunday night.
The storm system that the NHC is watching will make its way to Florida on Saturday. As it drifts across the same area hit by Hurricane Irma, it will soak the southern half of of Florida with heavy rain.
By Sunday morning, the amplified upper-level trough in the jet stream — the level that airplanes fly — will dip far enough south to launch the system rapidly up the East Coast. If this trough moves through faster, it could send the tropical low out into the Atlantic and have no impact on the Northeast.
The low-pressure center is likely to emerge off the coast of Florida early Sunday. As it does, it will gather energy and strength from a few different places: The same upper-level system will aid in bringing with it what is called a jet streak — which simply means an area of very confined very fast winds. The storm will gather fuel from the warm ocean temperature in the Gulf Stream and it will pick up speed from a weak point in the surface pattern.
But wait, there’s more.
At the surface — the part of the atmosphere we experience — a cold front will swing through the eastern half of the US. This system is typical this time of year and brings rain, sometimes severe storms and behind it, cold crisp air. The timing of the front moving through the Northeast will either move faster than forecast and protect the East Coast from the low off the coast of Florida, or it will line up perfectly and act as a bowling lane with the pins set up in the Northeast.
Most of the impacts, again, depend on timing and location. However, some things are inevitable.
Florida will get an increased amount of rainfall throughout the day on Saturday. Everywhere along the East Coast from Florida to Maine will experience rain to some varying degree between Saturday and Monday.
If the low pressure moves up the East Coast, there will be an increased amount of rainfall from Philadelphia to Boston. Very similar to a nor’easter, but without all of the snow. There will not be enough cold air in place to have snowfall along the coast. Either way, New York City residents will wake up Sunday wondering what happened to the sunny skies of the day before.
Temperatures in New York City will go from the upper 60s this weekend to the 50s on Monday.
Gusty winds will move in with the front on Sunday, but the ferocity of the winds speed is dependent on if the low tracks up the coast.
There is still a ton of uncertainty with this system. We are, thankfully, nearing the end of a very active hurricane season.
(But winter is just around the corner.)

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