Ike's storm surge an extreme danger to Texas

Hurricane Ike remains a huge a dangerous Category 2 hurricane, and has changed little since this morning. Ike's central pressure continues to hold steady at 950 mb, as measured by the Hurricane Hunters at 3:14 pm EDT. Ike's tiny 9-mile wide eye appears to be collapsing, which will allow a new eyewall of much larger-diameter to form. This event should allow Ike to start intensifying tonight. The latest Tropical Cyclone Heat Potential image shows that the center of Ike has just finished crossing a cold eddy in the Gulf of Mexico waters, and is now beginning to pass along the north side of a warm eddy. This change in oceanic heat should also help allow Ike to intensify tonight. The eddy is not ideally positioned, though, for rapid intensification to occur. The eddy is on the left (weak) side of the hurricane, where wind speeds are slower since the forward motion of the storm subtracts from the wind speed of the circulation. These lower-speed winds will be able to evaporate less moisture from the warm ocean than if the eddy were positioned on Ike's right side. Oceanic heat content remains moderately high after Ike crosses the eddy, which should allow some modest strengthening to continue. Wind shear of 10-15 knots and dry air on Ike's west side is hampering Ike slightly, as evidenced by the lack of upper-level outflow on the storm's west side and lack of heavy thunderstorm activity. Shear is expected to decrease to 5 knots by the time of landfall Saturday morning, and I expect Ike will be maintaining its strength or slowly intensifying right up until landfall. Ike will probably be at the top end of Category 2 strength at landfall, with 110 mph winds.

Comparisons to Carla and Katrina
Ike is larger than Katrina was, both in its radius of tropical storm force winds--275 miles--and in it radius of hurricane force winds--115 miles. For comparison, Katrina's tropical storm and hurricane force winds extended out 230 and 105 miles, respectively. Ike's surge will probably rival the massive storm surge of Hurricane Carla of 1961. Carla was a Category 4 hurricane with 145 mph winds at landfall, and drove a 10 foot or higher storm surge to a 180-mile stretch of Texas coast. A maximum storm surge of 22 feet was recorded at Port Lavaca, Texas. Despite the fact that the center of Carla hit over 120 miles southwest of Houston, the hurricane drove a 15-foot storm surge into the bays along the south side of the city. Ike's maximum surge is not likely to reach the extreme values above 20 feet seen in Hurricane Carla, though.


Figure 1. Experimental storm surge heights for Ike. There is a 10% chance the storm surge from Ike will exceed these values. Data courtesy of NOAA.

The total energy of Ike
The amount of water Ike has put in motion is about 10% greater than what Katrina did, and thus we can expect Ike's storm surge damage will be similar to or greater than Katrina's. The way we can estimate this damage potential is to compute the total energy of Ike's surface winds (kinetic energy). To do this, we must look at how strong the winds are, and factor in the areal coverage of these winds. Thus, we compute the Integrated Kinetic Energy (IKE) by squaring the velocity of the wind and summing over all regions of the hurricane with tropical storm force winds or higher. This "Integrated Kinetic Energy" was recently proposed by Dr. Mark Powell of NOAA's Hurricane Research Division as a better measure of the destructive power of a hurricane's storm surge than the usual Category 1-5 Saffir-Simpson scale. For example, Hurricane Katrina hit Mississippi as a strong Category 3 hurricane, yet its storm surge was more characteristic of a Category 5 storm. Dr. Powell came up with a new scale to rate potential storm surge damage based on IKE (not to be confused with Hurricane Ike!) The new scale ranges from 1-6. Katrina and Wilma at their peaks both earned a 5.1 on this scale (Figure 2). At 12:30pm EDT today, Ike earned a 5.2 on this scale, the second highest kinetic energy of any Atlantic storm in the past 40 years. Hurricane Isabel of 2003 had the highest. Note that the figures I quoted in this morning's blog saying Ike had an IKE of 180, 50% higher than Katrina's, were found to be in error due to some bad data from one of the Hurricane Hunter observations (the IKE is an experimental product, after all). Thus, this morning's IKE was actually a little lower than Katrina's.


Figure 2. Comparison of the potential damage from storm surge and waves on a scale of 1 to 6 (left scale, and corresponding to little "x" marks on the plot), as a function of total Integrated Kinetic Energy in Tera-joules (IKE, on the right scale, corresponding to the little squares on the plot). Hurricane Ike at 12:30pm EDT had an IKE of 134, 10% higher than the value of 122 Katrina had at landfall in Mississippi. Ike's amount of wind energy can generate storm surge and wave damage rated at 5.2 on a scale of 1 to 6, worse than Katrina's 5.1 at landfall. Image credit:"Tropical Cyclone Destructive Potential by Integrated Kinetic Energy" by Mark Powell and Timothy Reinhold.

Ike's waves
All this energy is also going into the waves in the Gulf of Mexico, and the offshore oil rigs can expect to receive a terrific battering. At 1:50pm CDT, waves at the buoy 42001 180nm south of Louisiana peaked at 30 feet. NHC is predicting Ike's waves will peak at 50 feet (15 meters) in the northern Gulf on Friday. For comparison, Hurricane Ivan of 2004 generated 27 meter (89 foot) high waves in the Gulf of Mexico. The oil companies spent hundreds of millions of dollars upgrading their oil rigs in the Gulf in the wake of the destruction wrought by Ivan and Katrina and Rita, and I'm not anticipating severe damage to the rigs from Ike's 50-foot waves.

Ike's storm surge
According to the NOAA tide gauges, the storm tides along the Mississippi coast have peaked at 4 feet above normal, and are currently running 5 feet above normal on the east side of New Orleans at Shell Beach in Lake Borgne. A storm surge of 5.9 feet was observed in New Orleans' Industrial Canal at 10:45 am CDT, and 5.75 feet in Waveland, Mississippi. Coastal Alabama is reporting a 4-6 foot storm surge, with 10-15 foot waves. Considering the center of Ike is over 250 miles south of these locations, it is not hard to imagine that Texas will get a 15-20 foot storm surge, even if Ike does not strengthen.

Ike will probably inundate a 250-mile stretch of Texas coast from Port O'Connor to the Louisiana border with a 10-15 foot storm surge. This will occur even if Ike is a Category 1 storm at landfall. If Ike is a Category 3+ hurricane at landfall, surges of 20+ feet are possible. The latest experimental storm surge forecast From NOAA's SLOSH model (Figure 1) shows a 10% chance that Ike's storm surge will exceed 18-21 feet at Galveston. The Galveston sea wall is 17 feet high, so it may get overtopped. At noon today, a mandatory evacuation of the entire island was ordered in case this worst-case scenario is realized. The official NHC forecast is calling for maximum storm surge heights of 20 feet.

What should Texas residents do?
We must assume Ike will intensify to a Category 3 hurricane by landfall, which would likely do $20-$30 billion in damage. Ike's storm surge is going to be affect a huge area and be tremendously destructive. The latest Hurricane Local Statement from the Galveston National Weather Service office puts things in pretty stark perspective:

All neighborhoods... and possibly entire coastal communities... will be inundated during high tide. Persons not heeding evacuation orders in single family one or two story homes will face certain death. Many residences of average construction directly on the coast will be destroyed. Widespread and devastating personal property damage is likely elsewhere. Vehicles left behind will likely be swept away. Numerous roads will be swamped... some may be washed away by the water. Entire flood prone coastal communities will be cutoff. Water levels may exceed 9 feet for more than a mile inland. Coastal residents in multi-story facilities risk being cutoff. Conditions will be worsened by battering waves. Such waves will exacerbate property damage... with massive destruction of homes... including those of block construction. Damage from beach erosion could take years to repair.

I recommend Texas residents consult NHC's wind probability product to determine their odds of getting hurricane force winds.

For storm surge evacuation zone information, consult the Texas Division of Emergency Management.

For storm surge heights, consult our Storm surge risk for the Texas coast page.

Links to follow
Galveston, TX weather

Tide gauges along the Gulf Coast

Mid Gulf Buoy 180 nm South of Southwest Pass, LA (42001)

Tropical disturbance 91L north of Puerto Rico
An area of disturbed weather (91L) has developed a few hundred miles north of Puerto Rico. Satellite loops show that 91L has a very small amount of heavy thunderstorm activity, but does have a circulation at middle levels of the atmosphere. A surface circulation is not apparent, but the mid-level spin could work its way down to the surface over the next day or two. The disturbance in under about 20 knots of wind shear, and is also having trouble with some dry air to the west. Shear is expected to remain 10-20 knots though Saturday, then increase to 25 knots. We may expect some slow development until Saturday, when wind shear should be too high to allow further development. None of the models are developing 91L. By Tuesday, as 91L will be approaching the east coast of Florida, shear is expected to decline to 15 knots, and some additional development may be possible, if the disturbance holds together that long.

I'll have an update tonight if there's a significant change in Ike.

Jeff Masters