Beginning this hurricane season, the National Hurricane Center will begin issuing separate watches and warnings for storm surge and winds.
The separate watches and warnings will mean, “we can issue the warning more precisely where hazard will be,” says Jamie Rhome, the National Hurricane Center’s storm surge lead. “Another big advantage is it’s clear the understanding and awareness of storm surge is not very high. Storm surge is the big killer. We need to raise the awareness of storm surge.”
Rhome says the separate storm surge watches and warnings will be considered to be experimental this year and in 2016. The goal is to collect responses from emergency managers and others affected by tropical storms and hurricanes. “If everything is favorable the product would become operational at the end of the experimental phase, which is the end of 2016,” Rhome says.
Since the well-known Saffir-Simpson hurricane scale was introduced to the public in 1973, with categories from 1 to 5 based on a hurricane’s maximum wind speed, many who live along the U.S. Gulf and Atlantic coasts, especially in areas that hurricanes hit most often, have come to base their evacuation decisions as much on a hurricane’s category as on official watches and warnings.
In fact, until 2009 the Hurricane Center’s description of each of the five categories included descriptions of the depth of storm surge likely for each category. For example, a 2001 description of what to expect from a category 2 hurricane said, “Storm surge generally 6-8 feet above normal.”
Nevertheless, Hurricane Ike, which hit Texas in 2008 as a category 2, brought up to 20 feet of storm surge, killing at least 20 people and leaving more than $30 billion in damage.
Hurricane Ike was a perfect illustration of the dangers of focusing on a storm’s category to decide whether to flee from places near the ocean or bays opening into the ocean well before a hurricane is forecast to arrive. The “it’s only a category 2 hurricane, why worry” attitude helped keep many from leaving Galveston Island and other locations near the Gulf of Mexico or Galveston Bay ahead of Ike even after the National Hurricane Center warned: “All neighborhoods … and possibly entire coastal communities … will be inundated during the peak storm tide. Persons not heeding evacuation orders in single family one- or two-story homes will face certain death.”
In contrast to Ike, Hurricane Charley, with hurricane force winds extending maybe 25 miles from the center, struck southwest Florida in 2004 as a category 4 with sustained winds of 140 mph, but produced a peak storm surge of only about seven feet.
In both cases the storm surge figures were far from the ranges that had been listed for their categories.
Rhome offers a simple “experiment” to show how the difference in storm size creates different surge heights. You can use a bathtub full of water or stand in waist-deep water in a swimming pool: “Push your arm through the water and then push one finger through the water. In both cases see how much water you move.”
In their previous descriptions of Saffir-Simpson categories, the National Hurricane Center explained how the depth and shape of the bottom of the ocean a hurricane is moving over as it hits land effects surge; “For example, if Hurricane Ike had made landfall in Palm Beach, Florida, the resulting storm surge would have been only 8 feet rather than the 20 feet that occurred where Ike actually made landfall on the upper Texas coast.” This is mainly because the Gulf of Mexico is relatively shallow off Galveston while the bottom of the Atlantic Ocean off West Palm Beach is deeper than the Gulf off Galveston.
The center removed figures for likely surge heights from its descriptions of the categories in 2009.
The new storm surge watches and warnings are not to be confused with the potential storm surge flooding maps that the center begin issuing last year. The potential maps show the worst surge flood that would be likely to occur if a hurricane hits a particular part of the coast.
These maps, which were first used for Hurricane Arthur this past July — the only tropical storm or hurricane to hit the U.S. in 2014 — give a heads up on what is possible from a particular tropical storm or hurricane before a surge watch or warning is issued. They will help officials and residents plan what to do if and when a surge watch or warning is issued and where the greatest danger is likely to be.
The Hurricane Center says the new storm surge warning shows where there is a danger of life-threatening inundation moving inland from the coast somewhere in the warned area within the next 36 hours. A storm surge watch means that threatening flooding is possible somewhere within the warned area generally within 48 hours.
“All persons, regardless of whether or not they are in the highlighted areas shown in the graphic should promptly follow evacuation orders from local officials,” the Hurricane Center says.
Rhome says “the reaction to the storm surge potential map was overwhelmingly positive” and while “it did highlight the hardest-hit areas,” but “it needs to be refined.” He notes that that this year’s surge watch and warnings will not be “official,” but are “a step in the step of a phased implementation toward an NWS storm surge warning system.
“Like a warning, however,” he says, “the graphic is intended to identify and help users visualize the areas most at risk from life-threatening surge, and serves as a call to action. It is also intended to stimulate initial feedback from users and partners by introducing the concept of a separate NWS warning for storm surge.”
While the surge watches and warnings won’t be “official’ this year and in 2016, if you happen to be in an area for which an “experimental” surge watch or warning is issued, you should head inland for higher ground.