Ike closes in on Galveston

Hurricane Ike is hours away from landfall on the upper Texas coast, and is already generating huge storm surges in Texas and Lousiana. Although still of Category 2 strength, Ike remains larger and more powerful than Category 5 Katrina or Category 5 Rita. As I discussed in yesterday's blog entry, a good measure of the storm surge potential is Integrated Kinetic Energy (IKE). Ike's Integrated Kinetic Energy has fallen from 149 Terajoules this morning to 124 at 3:30 pm EDT this afternoon. However, this is still larger than the total energy Katrina had at landfall, and Ike's storm surge potential rates a 5.1 on a scale of 1 to 6.


Figure 1. Image of Hurricane Ike from the International Space Station. Image credit: NASA.

The forecast
Ike is attempting to create a new eyewall, and visible satellite loops and Galveston radar suggest the storm is becoming more organized. However, Ike has only a few more hours over water, and there is not time for the hurricane to intensify more than 5-10 mph before landfall. Ike will not inflict extreme wind damage like Katrina's or Rita's. The big story with Ike will be the storm surge.


Figure 2.Current tide levels in Galveston. The green line shows the current storm surge, which was 7.5 feet at 4 pm CDT. The water level stopped rising at 2 pm because the tide began going out. When high tide comes back in at 2 am, there will be a sharp rise in the water level. There is a 2 foot difference between high tide and low tide. Image credit: NOAA TIdes and Currents.

Ike's storm surge
According to the NOAA tide gauges, storm tides are running 6-8 feet above normal along the central Louisiana coast this afternoon. The nola.com web site is reporting that a 9 foot storm surge affected the Industial Canal in New Orleans. Extensive flooding of low lying towns outside the New Orleans levee system is occurring. Surge overtopped a St. Mary Parish levee near the town of Gordy, and a six-foot-wide breach was reported in a non-federal parish levee near the towns of Caernarvon, Scarsdale, White Ditch and Braithwaite.

The fact that Ike's storm surge has reached such high levels 200-300 miles north of the storm is a very bad omen for the upper Texas and western Louisiana coasts. The latest forecast surge values from NOAA:

Shoreline of Galveston Bay... 15 to 22 feet
Bolivar Peninsula... 17 to 20 feet
Galveston Island... ... 14 to 17 feet
Gulf-facing coastline from Sargent to San Luis Pass... 8 to 14 feet

I've given the mistaken impression that the Galveston sea wall will save the city from inundation. That is not the case. The wall merely protects the city from a frontal assault by the storm surge and the 20 foot waves likely to be on top of the surge. Ike will flood the city of Galveston. However, the predicted level of surge will be just beneath the sea wall. If the surge exceeds the 17 foot forecast, it will overtop the sea wall and act like a battering ram against the buildings in Galveston. It is also possible that the sea wall will be destroyed along some sections, allowing the ocean direct access to Galveston.

The situation is also grim for Port Arthur, Texas, on the Louisiana border. The expected storm surge of 15-20 feet will overtop the city's seawall by six feet, resulting in flooding of the city and a number of major oil refineries. Expect a significant tightening of gas supplies in coming months, due to extensive damage to the oil refineries in the Houston and Port Arthur area.

Ike's winds in Houston and inland
Winds in the Houston metro area will increase to tropical storm force--39 mph--early this evening, and remain that strong for about 20 hours. Houston will be on the left (weak) side of Ike, and will miss the storm's strongest winds. Nevertheless, winds of Category 1 hurricane force (75-85 mph) will affect the city for about a 4-hour period in the early morning hours of Saturday. People in well-built homes will suffer only minor damage, but mobile homes and homes not build to code will suffer significant damage. The extremely long duration of the hurricane force winds will cause much greater damage than is typical for a hurricane of this strength.

Winds and damage in Houston will be less than was experienced during Hurricane Alicia of 1983. Ike's damage will cover a much wider area and spread farther inland, due to the large size of the storm. During Alicia, Houston Hobby Airport on the south side of the city recorded top winds of 89 mph, gusting to 99 mph. The strongest winds recorded at Houston International Airport, on the north side of the city, were 51 mph, gusting to 78 mph. Winds from Ike will probably reach maximum sustained speeds of 75-80 mph at Houston Hobby, and 65-70 mph at Houston International Airport.

A good guess on what kind of winds inland areas will experience can be had by using the Inland Wind Model developed by NOAA scientists Mark DeMaria and John Kaplan. This simple model shows the expected winds inland from the coast for the five Category hurricanes moving at different speeds. Plotted below (Figure 3) is the inland wind model plot that best fits the type of winds I expect will penetrate inland from Ike. I think Ike will be a strong Category 2 hurricane moving at about 15 mph at landfall, but the hurricane's strongest winds will penetrate farther inland than is typical due to the huge size of the storm. Thus, I picked a slightly stronger storm with a higher forward speed to base my inland wind estimate on. I expect hurricane force winds of 74 mph will penetrate about 110 miles inland, near the cities of Huntsville and Livingston to the north of Galveston, and not quite reaching Lufkin. We can expect Ike to cause the largest and longest-lived power outage in Texas history, with power knocked out along a 200-mile wide swath in eastern Texas and extreme western Louisiana extending 300 miles inland to I-20. Dallas will be at the fringe of the region of widespread power outages, and should not suffer major power failures.


Figure 3. Inland penetration of tropical storm and hurricane force winds from a Category 3 hurricane with 120 mph winds moving perpendicular to the Gulf Coast at a forward speed of 17 mph. Image credit: NOAA.

For more information
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
Port Arthur, TX weather
Houston, TX weather
Tide gauges along the Gulf Coast
Long-range radar out of Galveston, TX
wundermap of weather stations near Ike
Buoy 42035 22 nm SE of Galveston
I-45 traffic cams (bottom 6 on scroll-down menu are Galveston).

Tropical disturbance approaching the central Bahamas
An area of disturbed weather (91L) is located about 400 miles east of the central Bahamas, and is moving west-northwest at 10-15 mph. Satellite loops show that 91L's heavy thunderstorms have continued to increase in areal coverage this afternoon. However, these thunderstorms are not well organized, and there is no evidence of a surface circulation yet on visible satellite imagery.

The disturbance is under about 10 knots of wind shear, and is also having trouble with some dry air to the west. There is an upper-level low pressure just to the west of 91L that is creating shear and pumping dry air into the system, similar to the situation Hanna had to deal with in its formative stages. Shear is expected to remain 10-20 knots though Monday, which may allow some gradual development. None of the models are developing 91L, but the central Bahamas can expect heavy rain and strong gusty winds Saturday. These conditions may spread to the western Bahamas by Sunday and the east coast of Florida by Monday. NHC is giving this disturbance a low (<20% chance) of developing into a tropical depression by Sunday. A Hurricane Hunter aircraft is on call to fly into 91L on Sunday, if necessary.

Jeff Masters