5 Major Changes In 2017 Coming to Hurricane Season Forecasts

As the 2017 Hurricane Season approaches the NHC has announced 5 major changes coming in 2017, with some of the improvements having been in the works for decades!

1.) The Issuing Of Watches, Warnings and Advisories Before Storms Even Form.

The NHC will issue advisories for systems that have yet to develop but pose a threat of bringing tropical-storm-force or hurricane-force winds to land areas within 48 hours. These systems will be dubbed “potential tropical cyclones” by the NHC. Under previous longstanding NWS policy, it has not been permitted to issue a hurricane or tropical storm watch or warning until after a tropical cyclone had formed. Advances in forecasting over the past decade or so, however, now allow the confident prediction of tropical cyclone impacts while these systems are still in the developmental stage. For these land-threatening “potential tropical cyclones”, NHC will now issue the full suite of text, graphical, and watch/warning products that previously has only been issued for
ongoing tropical cyclones.

The “potential tropical cyclones” will be treated like tropical depressions, named storms and hurricanes. NHC will produce a forecast projected path, watches and warnings and text products, including a full discussion and the forecast advisory every six hours until the threat ends. Advisories will be issued for potential tropical cyclones at 5 a.m., 11 a.m., 5 p.m. and 11 p.m. EDT. Here is an Example of a Potential Tropical Cyclone Public Advisory.

Ed Piotrowski‏ on Twitter @EdPiotrowski @NHCDirector: “In 2017, advisories will be issued for potential tropical cyclones, especially for those close to land” #SCEMA17

2.) Time of Arrival of Tropical-Storm-Force Winds Experimental Graphic

The arrival time of Tropical Storm forced winds are critical especially for coastal communities since many preparedness precautions and activities become dangerous after these winds arrive. The NHC will be directly forecasting when tropical-storm-force winds will begin by issuing in 2017 an experimental Time of Arrival of Tropical-Storm-Force Winds graphics.

These graphics will be driven by the same Monte Carlo wind speed probability model that is currently used to determine the risk of tropical-stormand hurricane-force winds at individual locations – a model in which 1000 plausible scenarios are constructed using the official NHC tropical cyclone forecast and its historical errors.

The primary graphic displays the “earliest reasonable” arrival time, identifying the time window that users at individual locations can safely assume will be free from tropical-storm-force winds. Specifically, this is the time that has no more than a 1-in-10 (10%) chance of seeing the onset of sustained tropical-storm-force winds – the period during which preparations should ideally be completed for those with a low tolerance for risk. A second graphic will show the “most likely” arrival time – that is, the time before or after which the onset of tropical-storm-force winds is equally likely. This would be more appropriate for users who are willing to risk not having completed their preparations before the storm arrives.

Users will also be able to overlay the standard wind speed probabilities, providing a single combined depiction of the likelihood of tropical-storm-force winds at individual locations, along with their possible or likely arrival times. An example of these graphics is shown below.

3.) The Cone of Uncertainty Will Be Smaller

Each year, the NHC adjusts the size of its cone of uncertainty based on its average error over the previous five hurricane seasons. The cone of uncertainty refers to the projected path map you frequently see on the internet or television for a given storm.

The cone encapsulates 66 percent of the historical forecast track errors, and does not represent where impacts like surge, wind, flooding or tornadoes will be felt.

For the 2017 Atlantic hurricane season, the NHC will use the average track error for the 2012-2016 hurricane seasons. Track errors have gone down over the last 10 years and forecasts have gotten better as well. In fact, since 2007, the size of the cone of uncertainty at 120 hours (or five days) has shrunk by more than 35 percent. Since last year, the size of the cone at five days has shrunk by more than 10 percent. Similar reductions in size were seen from 2016 to 2017.

4.) Storm Surge Watch/Warning Becomes Operational

The National Weather Service (NWS) will issue storm surge watches and warnings for the Atlantic and Gulf coasts in the event that significant risk of life-threatening inundation develops from any stage of a tropical, subtropical or potential cyclone.

According to the NHC, ” Storm surge is often the greatest threat to life and property from a tropical cyclone, and it doesn’t always occur at the same times or locations as a storm’s hazardous winds.”

The definitions for the new storm surge watch and warning are:

Storm Surge Watch: The possibility of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 48 hours, in association with an ongoing or potential tropical cyclone, a subtropical cyclone, or a post-tropical cyclone. The watch may be issued earlier when other conditions, such as the onset of tropical storm-force
winds, are expected to limit the time available to take protective actions for surge (e.g., evacuations). The watch may also be issued for locations not expected to receive life-threatening inundation, but which could potentially be isolated by inundation in adjacent areas.

Storm Surge Warning: The danger of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 36 hours, in association with an ongoing or potential tropical cyclone, a subtropical cyclone, or a post-tropical cyclone. The warning may be issued earlier when other conditions, such as the onset of tropical storm force
winds, are expected to limit the time available to take protective actions for surge (e.g., evacuations). The warning may also be issued for locations not expected to receive life threatening inundation, but which could potentially be isolated by inundation in adjacent areas.

5.) Improved Tropical Cyclone Advisory Graphical Products

The NHC has updated the look of its tropical cyclone advisory graphics. The suite now has a consistent look across the various graphics, with cleaner fonts and softer colors. One significant enhancement is the addition of the current extent of hurricane- and tropical-storm-force winds to the cone graphic, which will help illustrate that hazardous conditions can occur well outside of the
track forecast cone. In addition, a set of radio buttons will allow users to toggle on and off various elements of the cone graphic. Examples of the NHC tropical cyclone graphics can be found at: http://www.nhc.noaa.gov/aboutnhcgraphics.shtml

(Old Graphic)

You can view the entire PDF announcement here: http://www.nhc.noaa.gov/news/20170309_pa_2017SeasonChanges.pdf