By Jim Stefkovich, Meteorologist, Alabama Emergency Management Agency
CLANTON –Tuesday, June 8, 2021
Part 1 on Monday focused on developing a hurricane action plan. If you missed it, it can be found here: https://ema.alabama.gov/2021/06/07/its-hurricane-season-and-time-to-prepare-in-alabama-part-1/ Part 2 will focus on receiving reliable forecasts, misconceptions and how to use these forecasts.
The first thing I want to stress is that you should receive critical weather information from the National Hurricane Center https://nhc.noaa.gov , the National Weather Service https://weather.gov , your local Emergency Management, and/or a trusted media source. Beware of social media sites! The graphic shows a few examples, including one that has the NOAA logo, and another that had over 77,000 “hits”. Shameful!
I also want to go over some misconceptions people may have about tropical storm and hurricane products.
The graphic below is from Hurricane Sally, which directly impacted a large portion of Alabama last September. The forecast cone of uncertainty represents the area where the center of storm will be. However, actual impacts, including storm surge, high winds, flooding rains and tornadoes often occur well outside the cone.
In addition, based on the past research, the center of the storm remains within the cone approximately 2/3 of the time. This also means that for any five day forecast, the center of the storm will NOT remain in the cone.
Why is this important to know? Because of what is called “anchoring”. At times, people don’t keep up to date with changing forecasts and anchor on a particular forecast which may be a few days old. They are then surprised to see changes right before landfall and are not prepared.
That’s why it’s important to constantly keep up to date with the latest forecasts from the National Hurricane Center (NHC) and your local NWS office.
Some storms are well defined and the forecast cones of uncertainty are much smaller. Other’s, like Sally, are much harder to predict both in landfall and intensity. The graphic below shows the large spread in computer model guidance on where Sally would make landfall.
In addition, just a few miles shift to the west or east can have tremendous impact differences as well.
Another useful product is the arrival time of “sustained” tropical-storm-force winds (39 mph – 73 mph) as shown below.
This arrival time is when substantial damage can begin with downed trees, power lines and building damage. All outdoor preparations should have been completed by this time or you should have already evacuated to a safer location.
There is a difference between sustained winds and gusts. Again, the earliest time of arrival is for sustained winds of 39 mph – 73 mph which lasts for a minute or more. Wind gusts can last a few seconds and arrive in rain bands well ahead of the sustained winds.
The point is, a tropical system’s rain bands often contain damaging high wind gusts, flooding rain and tornadoes well away from the sustained tropical-storm-force winds. You should consider having your action plan completed before the earliest time of arrival of the sustained winds.
The bottom line is to focus on the potential impacts of any storm and not the category. A tropical storm or category 1-5 hurricane is based on wind speeds ONLY. As we saw with Sally, many people were surprised just how much damage occurred, including well inland, from “just” a tropical storm.
Keep up to date frequently with the official forecasts, your local Emergency Management, and elected officials with the information they are providing through the web and media. The NHC and NWS are the only “official” forecasts. Any other sources should be rejected.
Finally, after the storm has moved through your area, be extremely cautious in dealing with the aftermath. There are more deaths after the storm has ended than direct impacts from the storm itself in some cases. This includes things like heart attacks, vehicle incidents, and improper use of generators (including carbon monoxide poisoning), to name a few.
It’s going to be an active season through the summer and early fall. There is no way to know if Alabama will be directly or indirectly impacted this year, but we must all be prepared. It’s not a question “if” Alabama will be impacted, it’s a question of “when”.