Friday, October 11, 2013

Catastrophic Storm Surge Imminent along Indian Coast

Tropical Cyclone Phailin tracking map provided by the Joint Typhoon Warning Center

 A catastrophic storm surge is imminent along the Indian Coast. At 0600 UTC this morning, the Joint Typhoon Warning Center placed the intensity of this storm at 135 kts (155 MPH), which puts it on the threshold between a category 4 and 5 tropical cyclone on the Saffir-Simpson Hurricane Wind Scale. Some slight intensification is forecast overnight (local time), so this storm should become a category-5 tropical cyclone.

It appears as though the intensity forecast has dropped off very slightly from the previous statement, but, in exchange the size of strong winds is forecast to increase, which could mean a larger storm surge overall. At 1800 UTC today, which should be approximately 18 hours before landfall, the storm is forecast to produce 140-kt winds (161 MPH), with a 35 nm radius of 64-kt winds. This means that hurricane-force wind speeds should extend about 35 nm from the center of circulation.

SCIPP has conducted multiple research projects that have proven that storm surge correlates better with tropical cyclone characteristics, like wind speed and storm size, before landfall than at landfall. The storm conditions 18 hours before landfall tend to correlate best with storm surge heights. This means essentially that a catastrophic storm surge is a certainty given the forecast intensity and size at 18 hours before landfall. Even if the cyclone suddenly started to weaken six hours from now (16 hours before landfall), a devastating storm surge would have already been set in motion.

This size is still a bit on the small size, but the very intense wind speeds should still enable Phailin to produce a devastating storm surge. Remember that in U.S. history, we've had several small, but intense, hurricanes that generated catastrophic surges. In 1900, the Galveston Hurricane generated a 6.1-meter (20 foot) surge along the Texas coast. Although it was a relatively small storm, it was classified as a category-4 hurricane 18 hours before landfall. The 1935 Labor Day Hurricane was one of the smallest hurricanes to strike the U.S., but it produced a 5.49- meter (18 foot) surge in the Florida Keys. It was a category-4 hurricane 18 hours before landfall and strengthened into the first category-5 hurricane to make landfall in the U.S. Hurricane Camille in 1969 was also a relatively small storm, but generated a massive 7.5-m (24.6 foot) surge along the Mississippi Coast.

Given the intense pre-landfall winds, shallow bathymetry, and the increased forecast area of 64-kt winds, one would have to estimate that this storm has the potential to generate a 6-meter (approx 20 foot) surge. This means the sea level would rise by 6 m (20 ft), accompanied by destructive waves that would ride ON TOP OF this massive storm surge.

Precautions/ evacuations should be taken immediately near and to the northeast of the forecast landfall location.

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