National Hurricane Center using new products this season to help with probabilistic storm surge, wind hazards, and storm guidance

New this year - 60-hour point forecast, storm surge inundation forecast values, new local time zones for systems in the eastern Atlantic

National Hurricane Center using new products this season to help with probabilistic storm surge, wind hazards, and storm guidance
NHC Hurricane Season


Today marks the first official day of the 2020 Atlantic hurricane season, and NOAA is predicting an above average Atlantic hurricane season.

"We've had some storms already. It's a good reminder that storms could form close to you, and effect you in a short period of time, sometimes in only two or three days. For example, you're not always going to have the luxury of watching a storm move all the way across the Atlantic Ocean, like an Irma for a week or more," says Dr. Michael Brennan, Branch Chief Specialist Unit with the National Hurricane Center (NHC).

The 2020 Atlantic Hurricane Season Begins

The NHC has implemented new products this season to help with probabilistic storm surge, wind hazards, and storm guidance.

These changes include:

1) Graphical depiction of storm surge inundation values

NHC will begin providing an experimental graphic in 2020 that will depict the expected storm surge inundation values for the United States Gulf and Atlantic coasts, Puerto Rico, and the U.S. Virgin Islands that are provided in the tropical cyclone public advisory (TCP). These values represent the peak height the water could reach above normally dry ground somewhere within the specified areas.

"Historically storm surge has been responsible for about half of the fatalities in terms of tropical storms and hurricanes in the United States. Fresh water flooding is responsible for about another 20% to 25%. The winds only responsible for maybe about 10%. So, people pay a lot of attention to the wind, but it's really the water hazards that are the deadliest," states Dr. Brennan.

2) 60-hour forecast information

NHC will begin providing 60-hour track, intensity, and 34-kt and 50-kt wind radii forecasts. These forecasts will be included in the tropical cyclone forecast/advisory (TCM), tropical cyclone discussion (TCD), and referenced within the tropical cyclone public advisory (TCP). The 60-h forecast information will also be included on the NHC cone graphic and will be used in the computation of the NHC wind speed probabilities, time of arrival graphic and probabilistic storm surge products.

Dr. Brennan says, "We've added a 60-hour forecast point to our suite of the 5-day forecast period. Now we have a forecast there between the 48-hour and 72-hour times, which is helpful for systems especially that are making landfall, or is going to have land impacts in that time frame before expecting more intensification or a change in the track, it allows us to kind of depict that. It also helps with our probabilistic guidance for storm surge and wind hazards that people help use to make decisions."

3) New local time zones for systems in the eastern Atlantic

The NHC public advisories, tropical cyclone discussions, tropical cyclone updates, and some graphical products have used local time within the product header based on the time zone where the center of the tropical cyclone is currently located. For example, advisories for tropical cyclones centered in the central and western Gulf of Mexico have used Central Time, and those near the east coast of the United States or in the eastern Gulf have used Eastern Time. All other Atlantic basin tropical cyclone advisories have referenced Atlantic Standard Time. This however, can be problematic for systems affecting the Cabo Verde Islands or other locations in the northeastern Atlantic basin where locations are 3 to 4 hours ahead of Eastern Time. Beginning in 2020, systems located south of 25°N and east of 30°W will use Cape Verde Standard Time (GMT-1) and systems north of 25°N and east of 45°W will use Greenwich Mean Time (equivalent to Azores Summer Time). These times will be used for the public advisory (TCP), discussion (TCD), update (TCU), and all graphical products that use local time.

4) Annual update to the track forecast error cone

The size of the tropical cyclone track forecast error cone for the Atlantic basin will be mostly unchanged this year. The eastern Pacific basin cone graphic will be slightly larger from 36 to 72 h, and slightly smaller at 120 h. The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of imaginary circles placed along the forecast track (at 12, 24, 36 hours, etc.). The size of each circle is set so that two-thirds of historical official forecast errors over the previous five years (2015-2019) fall within the circle.

“The changes in the cone size is due to our forecast errors decreasing and that’s largely driven by improvements in model forecasts, in both regional and global models,” says Dr. Brennan.

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