There has been a lot of buzz regarding a few tweets from President Donald Trump and whether or not Hurricane Dorian would impact Alabama. My intent for this blog post is to provide context to the forecasts and weather graphics that are being shown across the internet.
So was President Trump right about this hurricane affecting Alabama? In some ways yes, in other ways no.
It all started with this tweet from Sunday:
At this point in time, Hurricane Dorian was approaching The Bahamas as a Category 5 hurricane with winds of 160 mph. Parts of this tweet are correct, others are not. President Trump was correct by saying this storm could hit harder than anticipated. Over the past few days, Dorian was overachieving some of the forecasts from the National Hurricane Center. However, the track of the storm (both direction and speed) were generally on-point. At that time, the storm was not forecast to hit Alabama, but the other states listed in the tweet were likely to be affected.
Judging by this tweet alone, some would wonder why Alabama was being mentioned. To answer that, we have to go back to when this storm first formed and where some forecast models projected it to go.
Below is map called a spaghetti plot. Each line on this map is an individual forecast model, and forecasters use maps like this to look for trends in forecasting.
This map is from forecast models that were run during the afternoon of August 27th, which was 4 days before the tweet above.
You can see that the line are very close together toward the bottom of the plot. This means that the forecast models don’t differ too much from each other, and therefore forecasters should have a high amount of confidence that the storm would be in that general area. But as time goes on, the lines become farther apart. Some of these lines stay out at sea, some make a landfall someone in Florida, and other go even farther west through Florida and into the Gulf of Mexico.
The latter of those models were the ones suggesting that Dorian could potentially impact Alabama. As a forecaster, it would make sense given this map and the general weather pattern that Dorian would eventually take a turn to the northeast. That means that if it could make it into the Gulf of Mexico, Dorian could possibly make a second landfall somewhere near the Florida Panhandle and may move north into Alabama.
The problem with that thought, given the map above, is that out to sea and a turn north before making it to the Gulf of Mexico are also possible options.
The key takeaway from spaghetti plots like this is that they show what could happen. The image is a tool used to make forecasts; not a forecast itself.
In the following days, spaghetti plots like the one above and other forecast models and tools began to suggest that a turn to the north would likely happen before before Hurricane Dorian could make it into the Gulf of Mexico.
This new information was reflected in official National Hurricane Center forecasts like the two below. They show the probability of hurricane force and tropical storm force winds. The forecast made at this time, 2 PM EDT on August 30, shows the highest probability of these conditions reaching Alabama compared to any other forecast made by the NHC. But even despite it being the highest, it shows only about a 30-40% chance of tropical storm force winds (39-73 mph) reaching the extreme southeastern corner of Alabama, and just a 5-10% chance of these winds reaching areas just west of Tuscaloosa, Alabama. The probability of hurricane force winds is even lower. Aside from maybe a small sliver of extreme southeast Alabama, the state had a less than 5% chance of seeing hurricane force winds (74 mph or greater)
An issue that many people have brought up about the President’s tweet is that when it was send on September 1st, National Hurricane Center forecasts had no impacts in Alabama. The tweet was sent at 9:51 AM in the morning, and here was the latest advisory at that time.
This shows the storm turning north after stalling in The Bahamas and paralleling the Florida, Georgia, and Carolina coasts.
This turned out to be a good forecast. Dorian has the potential to make a landfall near Cape Lookout, North Carolina tonight, but overall it has stayed very close to that forecast track.
This didn’t make national news until after a briefing at the White House Wednesday. During that briefing, President Trump showed a forecast map for Hurricane Dorian. There were two things about this map that caught the attention of meteorologists nationwide.
First, the map was from almost a week ago. This forecast, issued on Thursday August, 29, shows Dorian making landfall in Florida as a major hurricane and then turning north. The cone of uncertainty, which widens with time to compensate for potential forecast errors, reaches the Gulf of Mexico.
At the time of this briefing, Dorian was already north of that forecast track and approaching the Carolina Coast as a Category 2 hurricane. That map that President Trump showed was dated with old, and now useless information.
The second, and probably more important error with this map, is it had a black line extending from the cone into Alabama. This appendage was not part of the official forecast from the National Hurricane Center, which is shown below.
You can watch a video of yesterday’s briefing here.
So again, was President Trump correct about Hurricane Dorian affecting Alabama? The information available at the time of his Alabama tweet and White House briefing could suggest no. Forecasts were trending away from the Gulf of Mexico and were favoring a turn to the north near Florida’s east coast. However, some information early in Dorian’s life did suggest it was a possibility (just not a great one).
To me, whether or not saying this would impact Alabama was a mistake, a tweet sent on old information, or something else is not important to me. I do think there is an important learning opportunity from all of this though. Everyone should always pay attention to the latest forecast information, because as I showed above forecasts evolve over time. The president has a great team of National Weather Service and NOAA forecasters to keep him updated with the latest threats, and this helps him prepare to disaster relief efforts. You at home have us, Storm Team ABC, to keep you updated when severe weather threatens the Heart of Illinois.