If you’ve seen a hurricane forecast, you’ve probably seen a graphic like the one below for Tropical Storm Dorian (as of August 27, 2019, 8:00 am):
There’s a lot going on in this graphic, but let’s focus on the cone. This is the white shaded or polka-dotted part of the map that is shaped like, well, a cone. The cone, as described in the graphic, represents the probable path of the storm center. But let’s break it down even further.
The black circles in the center of the cone show the forecasted classification of the storm at the noted day/time. In this case, Tropical Storm Dorian is projected to remain a tropical storm (sustained winds 39-73 miles per hour) as it travels towards Florida.
The white shaded portion of the cone represents the potential track from the time the forecast is issued until three days out. It is shaded because there is more certainty in the forecast to three days out than there is to five days out, which is represented by the white dotted portion of the cone. Although forecasters are less sure of the storm track four to five days out, this can help with hurricane preparation. People living in or near the dotted part of the cone should be sure to take the appropriate cautionary measures. In some cases, like 2017’s Hurricane Irma, this is evacuation. However, Tropical Storm Dorian may not have the same devastating impact as Irma. Precautionary measures should include stocking up on nonperishable food, one gallon of water per person per day, and making sure to have a method of receiving weather information. A portable power bank for a cell phone is a good idea to have, so that you can keep your cell phone charged to make calls, send texts, and receive information from the National Weather Service. NWS also offers a weather radio app that can be downloaded from the iTunes store or Google Play. Of course, monitor your local forecast and listen to any advice given by local officials.
But why is the cone shaped like a cone? The closer in time to the forecast, the more confidence forecasters have in the storm path. The farther out you go, the more uncertain the storm path. The cone gets wider because it encompasses the wider range of tracks that the storm’s center could take.
It is important to remember that the cone does not represent the size of the storm, only potential tracks for the storm’s center. As the graphic says, hazardous conditions can occur outside of the cone! If you live near the edges of the cone, you, too, should prepare for stormy weather.
©2019 Meteorologist Margaret Orr
Image Source: https://www.nhc.noaa.gov/refresh/graphics_at5+shtml/204140.shtml?cone