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Irene an extremely dangerous storm surge threat to the mid-Atlantic and New England

By: Dr. Jeff Masters, 2:55 PM GMT on August 25, 2011

Back in 1938, long before satellites, radar, the hurricane hunters, and the modern weather forecasting system, the great New England hurricane of 1938 roared northwards into Long Island, New York at 60 mph, pushing a storm surge more than 15 feet high to the coast. Hundreds of Americans died in this greatest Northeast U.S. hurricane on record, the only Category 3 storm to hit the Northeast since the 1800s. Since 1938, there have been a number of significant hurricanes in the Northeast--the Great Atlantic hurricane of 1944, Hazel of 1954, Diane of 1955, Donna of 1960, Gloria of 1985, Bob of 1991, and Floyd of 1999--but none of these were as formidable as the great 1938 storm. Today, we have a hurricane over the Bahamas--Hurricane Irene--that threatens to be the Northeast's most dangerous storm since the 1938 hurricane. We've all been watching the computer models, which have been steadily moving their forecast tracks for Irene more to the east--first into Florida, then Georgia, then South Carolina, then North Carolina, then offshore of North Carolina--and it seemed that this storm would do what so many many storms have done in the past, brush the Outer Banks of North Carolina, then head out to sea. Irene will not do that. Irene will likely hit Eastern North Carolina, but the storm is going northwards after that, and may deliver an extremely destructive blow to the mid-Atlantic and New England states. I am most concerned about the storm surge danger to North Carolina, Virginia, Maryland, Delaware, New Jersey, New York, and the rest of the New England coast. Irene is capable of inundating portions of the coast under 10 - 15 feet of water, to the highest storm surge depths ever recorded. I strongly recommend that all residents of the mid-Atlantic and New England coast familiarize themselves with their storm surge risk. The best source of that information is the National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in to see the height above ground level a worst-case storm surge may go. If you prefer static images, use wunderground's Storm Surge Inundation Maps. If these tools indicate you may be at risk, consult your local or state emergency management office to determine if you are in a hurricane evacuation zone. Mass evacuations of low-lying areas along the entire coast of New Jersey, Delaware, Maryland, and Virginia are at least 50% likely to be ordered by Saturday. The threat to the coasts of New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, and Maine is less certain, but evacuations may be ordered in those states, as well. Irene is an extremely dangerous storm for an area that has no experience with hurricanes, and I strongly urge you to evacuate from the coast if an evacuation is ordered by local officials. My area of greatest concern is the coast from Ocean City, Maryland, to Atlantic City, New Jersey. It is possible that this stretch of coast will receive a direct hit from a slow-moving Category 2 hurricane hitting during the highest tide of the month, bringing a 10 - 15 foot storm surge.

Figure 1. The scene in Nassau in the Bahamas at daybreak today. Image credit: Wunderblogger Mike Theiss.

Irene a Category 3 over the Bahamas, headed northwest
Hurricane Irene tore through the Bahama Islands overnight, bringing hurricane-force winds, torrential rains, and storm surge flooding to Crooked Island, Long Island, Rum Cay, and Cat Island, which all took a terrific pounding. Eleuthera and Abaco Island will receive the full force of Irene's eyewall today, but the eyewall will miss capital of Nassau. Winds there were sustained at 41 mph, gusting to 66 mph so far this morning, and I expect these winds will rise to 50 - 55 mph later today. Wunderblogger MIke Theiss is in Nassau, and will be sending live updates through the day today. Winds on Grand Bahama Island in Freeport will rise above tropical storm force late Thursday morning, and increase to a peak of 45 - 55 mph late Thursday afternoon. Grand Bahama will also miss the brunt of the storm. Irene is visible on Miami long-range radar, and the outer bands of the hurricane are bringing rain to Southeast Florida this morning.

Irene is currently undergoing an eyewall replacement cycle, where the inner eyewall collapses, and a new outer eyewall forms from a spiral band. During this process, the hurricane may weaken slightly, and it may take the rest of today for a new eyewall to fully form. Satellite imagery shows a lopsided pattern to Irene, with less cloud cover on the storm's southwest side. This is due to upper level winds from the southwest creating about 10 - 20 knots of wind shear along the storm's southwest side. We can hope that the shear will be strong enough to inject some dry air into the core of Irene and significantly weaken it today, but I put the odds of that happening at only 10%. The most likely scenario is that Irene will complete its eyewall replacement cycle later today or on Friday, then begin intensifying again. Wind shear is expected to stay moderate, 10 - 20 knots, for the next three days, ocean temperatures are a very warm 29°C, and Irene has an upper-level high pressure system on top of it, to aid upper-level outflow. None of our intensity forecast models show Irene growing to Category 4 strength, though the last 4 runs of the ECMWF global model--our best model for forecasting track--have intensified Irene to a Category 4 hurricane with a 912 - 920 mb pressure as it crosses over Eastern North Carolina.

Track forecast for Irene
The models have edged their tracks westwards in the last cycle of runs, and there are no longer any models suggesting that Irene will miss hitting the U.S. The threat to eastern North Carolina has increased, with several of our top models now suggesting a landfall slightly west of the Outer Banks is likely, near Morehead City. After making landfall on the North Carolina coast Saturday afternoon or evening, Irene is likely to continue almost due north, bringing hurricane conditions to the entire mid-Atlantic coast, from North Carolina to Long Island, New York. This makes for a difficult forecast, since a slight change in Irene's track will make a huge difference in where hurricane conditions will be felt. If Irene stays inland over eastern North Carolina, like the ECMWF and GFDL models are predicting, this will knock down the storm's strength enough so that it may no longer be a hurricane once it reaches New Jersey. On the other hand, if Irene grazes the Outer Banks and continues northwards into New Jersey, like the GFS model is predicting, this could easily be a Category 2 hurricane for New Jersey and Category 1 hurricane for New York City. A more easterly track into Long Island would likely mean a Category 2 landfall there.

Category 2 landfalls may not sound that significant, since Hurricane Bob of 1991 made landfall over Rhode Island as a Category 2, and did only $1.5 billion in damage (1991 dollars), killing 17. But Irene is a far larger and more dangerous storm than Bob. The latest wind analysis from NOAA/HRD puts Irene's storm surge danger at 4.8 on a scale of 0 to 6, equivalent to a borderline Category 3 or 4 hurricane's storm surge. Bob had a much lower surge potential, due to its smaller size, and the fact it was moving at 32 mph when it hit land. Irene will be moving much slower, near 18 mph, which will give it more time to pile up a big storm surge. The slower motion also means Irene's surge will last longer, and be more likely to be around during high tide. Sunday is a new moon, and tides will be at their highest levels of the month during Sunday night's high tide cycle. Tides at The Battery in New York City (Figure 3) will be a full foot higher than they were during the middle of August. Irene will expand in size as it heads north, and we should expect its storm surge to be one full Saffir-Simpson Category higher than the winds would suggest.

Figure 2. Predicted tides for the south shore of New York City's Manhattan Island at The Battery for Sunday, August 28 and Monday, August 29. High tide is near 8pm EDT Sunday night. Tidal range between low and high tide is 6 feet on Sunday, the highest range so far this month. A storm surge of 10 feet would thus be 10 feet above Mean Lower Low Water (MLLW, the lowest tide of the year), but 16 feet over this mark if it came at high tide. Image credit: NOAA Tides and Currents.

Irene's storm surge potentially extremely dangerous for the mid-Atlantic coast
Irene's large size, slow motion, arrival at high tide, and Category 3 strength at landfall in North Carolina will likely drive a storm surge of 8 - 10 feet into the heads of bays in Pamlico Sound, and 3 - 6 feet in Albemarle Sound. As the storm progresses northwards, potential storm surge heights grow due to the shape of the coast and depth of the ocean, though the storm will be weakening. If Irene is a Category 1 storm as it crosses into Virginia, it can send a storm surge of 4 - 8 feet into Chesapeake Bay and Norfolk. I give a 50% chance that the surge from Irene in those locations will exceed the record surges observed in 2003 during Hurricane Isabel. The region I am most concerned about, though, is the stretch of coast running from southern Maryland to Central New Jersey, including Delaware and the cities of Ocean City and Atlantic City. A Category 1 hurricane can bring a storm surge of 5 - 9 feet here. Irene's large size, slow movement, and arrival at the highest tide of the month could easily bring a surge one Category higher than the storm's winds might suggest, resulting in a Category 2 type inundation along the coast, near 10 - 15 feet. This portion of the coast has no hurricane experience, and loss of life could be heavy if evacuation orders are not heeded. I give a 30% chance that the storm surge from Irene will bring water depths in excess of 10 feet to the coasts of Maryland, Delaware, and New Jersey.

Figure 3. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge along the Maryland, Delaware, and New Jersey coasts in a worst-case scenario. The image was generated using the primary computer model used by the National Hurricane Center (NHC) to forecast storm surge--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The accuracy of the SLOSH model is advertised as plus or minus 20%. This "Maximum Water Depth" image shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. This Maximum of the "Maximum Envelope of Waters" (MOM) image was generated for high tide and is a composite of the maximum storm surge found for dozens of individual runs of different Category 2 storms with different tracks. Thus, no single storm will be able to cause the level of flooding depicted in this SLOSH storm surge image. Consult our Storm Surge Inundation Maps page for more storm surge images of the mid-Atlantic coast.

Figure 4. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge along the New Jersey coast in a worst-case scenario. Water depths could reach 6 - 8 feet above ground level in Ocean City and Atlantic City, and up to 16 feet along less populated sections of the coast.

Irene's storm surge may flood New York City's subway system
The floodwalls protecting Manhattan are only five feet above mean sea level. During the December 12, 1992 Nor'easter, powerful winds from the 990 mb storm drove an 8-foot storm surge into the Battery Park on the south end of Manhattan. The ocean poured over the city's seawall for several hours, flooding the NYC subway and the Port Authority Trans-Hudson Corporation (PATH) train systems in Hoboken New Jersey. FDR Drive in lower Manhattan was flooded with 4 feet of water, which stranded more than 50 cars and required scuba divers to rescue some of the drivers. Mass transit between New Jersey and New York was down for ten days, and the storm did hundreds of millions in damage to the city. Tropical Storm Floyd of 1999 generated a storm surge just over 3 feet at the Battery, but the surge came at low tide, and did not flood Manhattan. The highest water level recorded at the Battery in the past century came in September 1960 during Hurricane Donna, which brought a storm surge of 8.36 feet to the Battery and flooded lower Manhattan to West and Cortland Streets. However, the highest storm surge on record in New York City occurred during the September 3, 1821 hurricane, the only hurricane ever to make a direct hit on the city. The water rose 13 feet in just one hour at the Battery, and flooded lower Manhattan as far north as Canal Street, an area that now has the nation's financial center. The total surge is unknown from this greatest New York City hurricane, which was probably a Category 2 storm with 110 mph winds. NOAA's SLOSH model predicts that a mid-strength Category 2 hurricane with 100-mph winds could drive a 15 - 20 foot storm surge to Manhattan, Queens, Kings, and up the Hudson River. JFK airport could be swamped, southern Manhattan would flood north to Canal Street, and a surge traveling westwards down Long Island Sound might breach the sea walls that protect La Guardia Airport. Many of the power plants that supply the city with electricity might be knocked out, or their docks to supply them with fuel destroyed. The more likely case of a Category 1 hurricane hitting at high tide would still be plenty dangerous, with waters reaching 8 - 12 feet above ground level in Lower Manhattan. Given the spread in the models, I predict a 20% chance that New York City will experience a storm surge in excess of 8 feet that will over-top the flood walls in Manhattan and flood the subway system. This would most likely occur near 8 pm Sunday night, when high tide will occur and Irene should be near its point of closest approach. Such a storm surge could occur even if Irene weakens to a tropical storm on its closest approach to New York City.

Figure 5. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge in a worst-case scenario in New York City.

Figure 6. Flooded runways at New York's La Guardia Airport after the November 25, 1950 Nor'easter breached the dikes guarding the airport. Sustained easterly winds of up to 62 mph hit the airport, pushing a large storm surge up Long Island Sound. The storm's central pressure bottomed out at 978 mb. Image credit: Queens Borough Public Library, Long Island Division.

The rest of New England
The entire New England coast is at high danger of receiving its highest storm surge in the past 50 years from Irene, though the exact locations of most danger remain unclear. If North Carolina takes a bullet for us and reduces Irene below hurricane strength before the storm reaches New England, the surge will probably not cause major destruction. But if Irene misses North Carolina and arrives along the New England coast as a hurricane, the storm surge is likely to cause significant damage. I urge everyone along the coast to familiarize themselves with their storm surge risk and be prepared to evacuate should an evacuation order be issued.

For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, and will be sending live updates through the day today.

Landstrike is an entertaining fictional account of a Category 4 hurricane hitting New York City.

Elsewhere in the tropics
Tropical Depression Ten in the far Eastern Atlantic will not be a threat to any land areas over the next seven days, and will probably move too far north to ever be a threat to land.

Portlight mobilizes for Irene
The Bahamas have been hit hard by Irene, and unfortunately, it appears that the Northeast U.S. may have its share of hurricane victims before Irene finally dissipates. My favorite disaster relief charity, Portlight.org, is mobilizing to help, and is sending out their relief trailer and crew to the likely U.S. landfall point. Check out this blog to see what they're up to; donations are always needed.

Jeff Masters
Irene in the Dominican Republic
Irene in the Dominican Republic
Flooding caused by Heavy Rains from Irene making the Rivers Rise and flooding nearby communities.
Irene in the Dominican Republic
Irene in the Dominican Republic
Flooding of the River Nigua in the Dominican Republic and people that were forced to leave their homes behind.
Hurricane Irene
Hurricane Irene
The sun peeking over the top of the eyewall
Hurricane Irene
Hurricane Irene
By the fourth pass, Irene had a pretty well developed eyewall


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