Hurricane season is fast approaching as it begins June 1st, just over a month from now. Earlier this week, the National Hurricane Center (NHC), which is responsible for the official hurricane forecasts for the United States, released a notice on any updates on NHC products and services.
Update to Track Forecast Error Cone:
The most significant of these updates is that the tropical cyclone track forecast error cone (“cone of uncertainty”) for the Atlantic basin will be smaller this year. NHC adjusts the forecast error cone every year by making it the same or either larger or smaller. According to NHC in their released document, “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 (2013–2017) fall within the circle.” What’s also interesting is that they made the forecast error cone for the eastern Pacific basin greater for the longer forecast times. The below chart shows the circle radii defining the cones in 2018 for the Atlantic and eastern North Pacific basins.
NHC Public Advisory Will Now discuss Forecast Information Beyond 48 Hours:
In the past, NHC Public Advisories, which contains a list of all current coastal watches and warnings and gives pertinent storm information, including general forecast and hazard (storm surge, wind, rainfall, tornadoes, surf) information, only contained forecast information for the next 48 hours. Now, these Public Advisories will provide information beyond the old 48 hour timeframe to provide better lead time for tropical cyclones. NHC states that “this change will allow public advisories to discuss the track and intensity forecast routinely through 72 hours, and allow the flexibility to discuss the forecast through 5 days when conditions warrant.”
Format of Weather Prediction Center (WPC) Public Advisories on Inland Depressions Will Now Mirror the format of NHC Public Advisories:
Before this point, WPC issued brief Public Advisories that contained information on rainfall and the potential for flash flooding when decaying tropical systems move into the US. These advisories are issued “when winds drop below tropical storm strength and the system is not forecast to regain tropical storm intensity or re-emerge over water,” according to NHC. Beginning this year’s hurricane season, WPC Public Advisories will now follow the same format of NHC Public Advisories. They will contain the same sections: Summary, Watches and Warnings, Discussion and Outlook, Hazards, and Next Advisory. This update will provide the public with more crucial information about these decaying tropical cyclones. These advisories will be issued every six hours, or four times a day, until not-needed anymore.
48-Hour Hurricane Force Wind Radii Forecast Will Be Issued:
Another important service beginning in 2018 will be the 48-hour hurricane force wind radii forecast. This forecast will provide the public with the forecast maximum extent of these winds in each quadrant of the storm. Not only will the hurricane force winds be forecast out to 48 hours, but the tropical storm force winds will be forecast out to 72 hours. This is another potentially life-saving tool that could increase the warning time for people in the potential path of a storm: “The addition of hurricane-force wind radii at 48 hours will improve the deterministic and probabilistic guidance for areas at risk from hurricane-force winds and can help forecasters facilitate the issuance of and determine the placement of a hurricane watch.”
The NHC Arrival Time of Tropical-Storm-Force Winds Graphics Will Become Operational in 2018:
The National Hurricane Center debuted new graphics in 2017 that were experimental, which provided the arrival time of tropical-storm-force winds. These graphics are also crucial, especially in terms of hurricane preparedness ahead of an incoming storm. These arrival times provide guidance on when users should consider having their preparations completed before a storm. These graphics come in two different versions. The primary graphic displays the “earliest reasonable” arrival time while the secondary graphic shows the “most likely” arrival time. The main difference between these two is the risk for tropical-storm-force winds. People in the path of a tropical cyclone should follow the primary graphic (“earliest reasonable” arrival times) which ensures that you will be able to finish all preparations to keep yourself safe before the arrival time shown in the graphic.
New Reconnaissance Vortex Message Format:
Last but not least, the sixth change NHC has made to their products and services this year is that there will now be a new reconnaissance vortex message format. Many of you likely have no idea what this means, but we’re here to explain it to you. These Vortex Data Messages provide information that the Hurricane Hunters gather. The new format will make the message more organized and will provide more information. The information provided in these messages include: latitude and longitude of location, surface wind reported by dropsonde (tool that detects wind) at the system’s center, center/eye shape and size characteristics, wind observation times and locations, inbound maximum surface wind, and flight-level wind. Here’s what the new reconnaissance Vortex Data Message will look like: