Irene sends 4.5 foot storm surge up Chesapeake Bay

The eye of Hurricane Irene is back over water, after the hurricane completed a 11-hour crossing of eastern North Carolina. Irene came ashore over Cape Lookout, North Carolina at 7:30 am EDT this morning as a Category 1 hurricane with 85 mph winds. The Cedar Island Ferry Terminal measured sustained winds of 90 mph, gusting to 115 mph at 7:19am, as measured by a Department of Transportation official. I suspect this measurement came when a thunderstorm near Irene's center collapsed, sending a powerful downburst to the surface. A trained spotter on Atlantic Beach, NC measured sustained winds of 85 mph, gusting to 101 mph at 10:35 am. The Hurricane Hunters measured 80 mph winds over water at the time of landfall. However, no regular weather station or buoy has measured sustained hurricane force winds in Irene, with the highest winds being 67 mph at the Cape Lookout, North Carolina buoy as Irene made landfall. Winds have peaked along the coast of Virginia, where sustained winds of 61 mph were observed at 6 pm EDT at Chesapeake Bay Light. Irene's passage over land weakened the storm slightly, and satellite loops show more dry air has wrapped into the storm. The radar presentation of Irene visible on the Norfolk, VA radar is still very impressive--Irene is dropping torrential rains over a huge area--but there is much less rain over the storm's southeastern quadrant, over water. Radar-estimated rainfall shows a 50 mile-wide band of 8+ inches of rain has fallen from where Irene made landfall at Cape Lookout, North Carolina, northwards to Dover, Delaware. Some isolated amounts of 15+ inches may have fallen, according to the radar estimates. Bunyan, NC has received 14.00" so far, and the towns of Washington, New Bern, Grifton, Newport-Croatan, Wonona, NC, all received more than ten inches. Norfolk, Virginia had received 7.73" as of 7pm EDT, and Suffolk, Virginia, 8.00".


Figure 1. True-color MODIS image of Hurricane Irene over North Carolina taken at 11:35 am EDT August 27, 2011. At the time, Irene was a Category 1 hurricane with 85 mph. Image credit: NASA.

Storm surge damage from Irene
The storm surge and wave action from Irene is likely to cause the storm's greatest damage. High tide is near 7 - 8 pm EDT tonight, meaning that the storm surges occurring now will be some of Irene's most damaging. The highest surges measured at any of NOAA's regular tide gauges at 8 pm were 4.5 feet at Sewells Point in Norfolk Virginia and Oregon Inlet, NC. Higher surges are occurring father inland where narrow inlets funnel the storm surge to higher elevations. It remains unclear if the ocean will overtop Manhattan's sea wall at The Battery Sunday morning during the 8 am high tide. Latest storm surge forecasts from SUNY Stony Brook predict a peak water level of 2.4 meters above Mean Lower Low Water (MLLW) at 7:15 am Sunday, which would put the ocean right at the top of the sea wall. Presumably, waves from the hurricane's winds would then push some water over the top of the wall, but it is uncertain whether or not this would cause significant flooding. The storm surge was already 1 foot at 8 pm tonight. Storm surge flooding continues to be a major concern all along the coast of Long Island Sound; I recommend the SUNY Stony Brook storm surge page for those interested in looking at observed and predicted storm surge levels along coast New Jersey, New York, and Connecticut.


Figure 2. Storm surge at Sewell's Point in Norfolk, Virginia as of 8 pm EDT Saturday August 27, 2011. The green line is the storm surge, which is the difference between the observed water level (red line) and what the water level should have been without the hurricane (blue line). At 8 pm, the storm surge was 4.5 feet. Image credit: NOAA Tides and Currents.


Figure 3. Distribution of Irene's wind field at 6:30 pm EDT Saturday August 27, 2011, as observed by the Hurricane Hunters, land stations, and buoys. The right front quadrant of the hurricane had all of the storm's shrinking hurricane-force winds (yellow and orange colors.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 290 miles from the center of Irene over water, but very few areas of land were receiving tropical storm force winds. Image credit: NOAA/AOML/HRD.

Wind damage
The emergence of Irene's eye over water will slow the storm's rate of weakening, but the storm is under too much wind shear to allow it to intensify. The latest wind distribution map from NOAA's Hurricane Research Division (Figure 3) shows that all of Irene's hurricane-force winds are on the storm's east side, and also the large majority of the tropical storm-force winds. When Irene makes its 2nd landfall on Long Island, NY on Sunday, coastal locations to the right of the eye will likely experience top sustained winds of 50 - 60 mph. Coastal areas of Maryland, Delaware, New Jersey, and the New York CIty area will mostly see top winds in the 40 - 55 mph range, since they will be on the weaker left side of the storm. Winds on the upper floors of skyscrapers will be up to 30% higher, but I expect there will be only isolated problems with New York City skyscrapers suffering blown out windows. The winds from Irene in New York City will be no worse than those experienced during some of the city's major Nor'easter winter storms of the past twenty years.

Tornadoes
Four tornadoes have been spawned by Irene, two in coastal North Carolina last night, and two in coastal Virginia today. At least two homes have been destroyed, and ten others damaged by the tornadoes. NOAA's Storm Prediction Center has issued a tornado watch for all of coastal Delaware, New Jersey, New York, and Connecticut.

Links
Our Weather Historian, Christopher C. Burt, has an excellent post on Historic Hurricanes from New Jersey to New England.

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.

Jeff Masters