Tropical Storm Hermine to get stuck near Mid-Atlantic due to a ‘Rex block’

Tropical Storm Hermine to get stuck near Mid-Atlantic due to a ‘Rex block’

Posted by John P. Bradford // December 29, 2016

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UPDATE: Sept. 3, 2016, 7:55 a.m. EDT Tropical Storm Hermine is emerging back over the unusually warm waters of the Atlantic Ocean, where it will morph into a hybrid storm system with tropical and non-tropical characteristics.

The storm is bringing “life-threatening inundation” to the Hampton Roads, Va. area on Saturday morning, and is still forecast to slam the Mid-Atlantic coast with major flooding, strong winds, and heavy rain.

Computer models overnight backed off slightly from the scenario of the storm backing well to the west, into the New Jersey coast, instead keeping it a bit further offshore. This could lessen the storm surge and wind speeds, but major impacts are still expected.

UPDATE: Sept. 2, 2016, 2:27 p.m. EDT Projections for the storm’s intensity and path are showing that even greater impacts are likely along the Mid-Atlantic coast than previously thought. There is now the real prospect of a top 3 flood event, unfolding over several days, from Virginia to New York, with the greatest threat in central and southern New Jersey.

The European model, which is historically among the most reliable forecast tools, is now showing the storm intensifying and moving west, backing into the Jersey shore.

If this were to happen and this is far from certain the storm surge would be significantly higher than many people were expecting even earlier today.

UPDATE: Sept. 2, 2016, 12:38 p.m. EDT Computer model projections are showing a more menacing scenario taking place along the Mid-Atlantic coast, with a westward jog from Hermine just as the storm re-intensifies into a hurricane.

If this plays out, major to possibly record coastal flooding could result at many locations.

Therefore, given the holiday weekend, meteorologists and others are beginning to advise travelers to cancel their plans to go to beaches in Virginia, Maryland, Delaware or New Jersey this weekend.

UPDATE: Sept. 2, 2016, 11:55 a.m. EDT Tropical storm watches have now been hoisted for New York City eastward to Watch Hill, Rhode Island. In addition, the latest guidance from the National Hurricane Center shows the storm re-intensifying into a hurricane off the coast of North Carolina, as it moves over the warm waters of the Gulf Stream on Monday.

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Original story:

At first glance, the storm track forecast for Tropical Storm Hermine might not raise many red flags if you’re living in the Mid-Atlantic or the Northeast.

It’s only when you realize that the storm is going to move less than 300 miles in three days that one sees what an anomaly this storm is likely to be.

The slow movement of the storm, along with its passage over bathtub-like Atlantic Ocean waters, raises red flags for Hermine. The storm could cause significant if not historic coastal flooding in parts of the Mid-Atlantic.

Here’s why.

A blocking pattern named Rex

A blocking pattern in the mid-to-upper atmosphere, known as a Rex Block, is going to prevent Hermine from moving harmlessly out to sea after it slips off the coast of North Carolina.

Such a blocking pattern consists of a high pressure area to the north of an area of low pressure (in this case that low is Hermine), which prevents much eastward movement of the low.

Scholars of Hurricane Sandy might remember that a blocking pattern was what captured that storm and flung it westward into the New Jersey coast, devastating that state in 2012.

While Hermine is not Sandy, both in terms of its intensity, size and the type of blocking involved, it could lead to a significant, if not a record, coastal flooding event in some spots.

Due to the blocking pattern, Hermine which may either be a post-tropical storm by that point or a fully tropical system is forecast to swirl around off the coast of southeastern New Jersey for about three days, allowing for the buildup of high seas and pounding of fragile shorelines.

Image: weatherbell analytics

The Weather Prediction Center in Maryland is calling for Hermine to “get stuck off the Mid-Atlantic coast for much or possibly all of the week.”

Some computer models on Friday were showing a potentially dire scenario in which the storm would re-intensify into a hurricane and hook west, into the Jersey Shore near Atlantic City, in a near-repeat of the path that Hurricane Sandy took.

The animation below shows one such model, the Euro, which is projecting that:

The fact that this scenario is on the table just 36 hours before the event moves into the area should concern homeowners, vacationers and any others with interests along the coast.

Milder than average ocean temperatures

Hermine is forecast to park itself on top of the unusually mild waters of the Gulf Stream.

Some of the most unusually mild water temperatures in all of the Atlantic Ocean right now are located off the Mid-Atlantic coast.

The precise temperature anomalies off the coast of New Jersey are 2 to 5 degrees Celsius, or 3.6 to 9 degrees Fahrenheit, above average. In fact, the waters off the New Jersey coast have been so warm that mass fish-kills have been reported this summer.

These warm water anomalies are likely due to both natural climate variability including the lack of major storms in this region that would have stirred up cooler waters from below while the shattering of global ocean temperature records indicates the effects of human-caused global warming.

Such unusually mild waters can add energy to a storm like this, potentially allowing it to re-intensify for a time. However, because the storm is going to stall for several days, its winds are likely to drag cooler waters up from deeper layers of the Atlantic through a process known as upwelling, which could then weaken it significantly by midweek.

Coastal flood guidance

While more precise coastal flood forecasts may not be known with high confidence until Saturday or Sunday, it is already abundantly clear from the information at hand that moderate to major coastal flooding is likely to occur from Virginia northward to New Jersey.

It is also possible that New York City, Long Island, coastal Connecticut, Rhode Island and Massachusetts will see damaging waves, beach erosion and coastal flooding from this storm.

Heavy rain and strong winds may also hit the coast in fits and starts, particularly from New York City southward to the Delaware shore.

According to the National Weather Service forecast office in Philadelphia, the uncertainty regarding the storm’s track and intensity remains high, but there is the potential for up to 6 inches of rain, tropical storm force winds and coastal as well as tidal flooding for the southeastern New Jersey and entire Delaware coasts.

This is not *quite* another Sandy, but…

In short, Hermine is not Hurricane Sandy. For one thing, it does not have the reach that Sandy did, given that the 2012 storm’s wind field was nearly 1,000 miles in diameter when it hit the Mid-Atlantic.

Image: weatherbell analytics

In addition, Hermine may be weaker than Sandy was, at least in terms of its central air pressure, which will help lower the storm surge slightly.

However, the areal coverage of Hermine’s wind field will broaden as it moves northward, rather than remaining tightly wound as it was when the storm first hit Florida.

Like Sandy did, this storm may also interact with non-tropical weather systems that could allow it to re-intensify as a hybrid tropical-post-tropical storm while it remains off the East Coast.

This is significant only to meteorologists, as the practical implications for people living along the coast are the same regardless of what type of storm it will be: windswept, occasional rain along with damaging coastal flooding and high surf.

Tropical Storm Hermine has the potential to do some significant damage, particularly if the track adjusts westward by as little as 50 miles compared to current forecasts.

Several computer models show the center of the storm could wobble westward while it is stalled out between Saturday and Wednesday, and this would greatly increase coastal impacts.

The prolonged nature of the onshore winds alone will mean that flooding could occur during multiple high tides, which increases the beach erosion and property damage potential.

Sea level rise

Sea level rise in the Mid-Atlantic is also going to amplify this storm’s damage potential. Due to human-caused global warming, land subsidence and ocean currents, sea levels have risen faster in the Mid-Atlantic than in many other parts of the world.

This means that any storm surge rides atop a higher baseline sea level,and can therefore due more damage than just a few decades ago.

In New York City, for example, the sea level is about a foot higher now than it was in 1900, which increases coastal flood risks.

This story is developing…

Read more: http://mashable.com/2016/09/02/hermine-coastal-flooding-mid-atlantic/