As mentioned in the last BMS Tropical Update, it’s a bit early to determine where hurricane Irma will be heading 10 to 15 days from now, which is when it could be eyeing a potential U.S. coastline impact. However, as much of the U.S. insurance industry heads into a long weekend, here is what my gut thinks will happen with Irma over the next 10 days.

When forecasting in the long range, it is important to look at what is occurring worldwide. There is a very good chance that Irma’s future track will be influenced by what is going on in the West Pacific. Currently there is a typhoon named Sanvu southeast of Japan. This typhoon is expected to recurve into the westerlies over the next few days.

Current location and track of Typhoon Sanvu in the West Pacific Ocean

There is a general rule of thumb in meteorology that when this occurs, it could cause a trough of low pressure to move towards the U.S. East Coast between 6 to 10 days later. This means that if the typhoon recurves as forecasted over the next few days, a trough of low pressure could potentially be on the East Coast sometime between September 7th and 11th. In fact, some global models are picking up on this trough of low pressure for next week. Some even produce the first frost of the season for parts of the Upper Midwest, so it will have some punch.
Around September 7th and 8th, Irma will be a major hurricane and will likely be a Category 4 or perhaps even a Category 5 over or near the Leeward Islands. This will result in three potential scenarios for later next week, based on the forecasted trough of low pressure and Irma’s latitude at that time:

  1. Irma could be at a high enough latitude that it gets pulled north by this trough of low pressure, similar to Gret’s path the second week of August, and recurve in between the U.S. and Bermuda.
  2. Irma could be at a low enough latitude that it misses getting pulled into the trough of low pressure and tracks south of Puerto Rico, perhaps into the Gulf of Mexico.
  3. If Irma is near the Northern Leeward Islands, it could get pulled up by the trough of low pressure, but miss the full connection, and head towards Florida and the East Coast with a close landfall threat later the following week.

Right now this might be the best graphic I have found on the future of Irma. Its based on the ECMWF Model, but it provides a good long range outlook at this time of the three opitons above. Source The Weather Channel


Based on the current forecast of Irma being a major hurricane near the Leeward Island next week here is a history of all the major hurricane over this forecasted area and where they tracked. It follows The Weather Channel guidance nicely, but keep in mind this is history and not a forecast.

At the start of the season, I thought the East Coast was going to be the biggest threat of landfalling storms in the U.S., and I don’t see a reason why that should change. Based on the forecast and history, there is currently a 60% chance of Irma impacting the U.S as at least a tropical storm, and  a 30% chance of seeing a major hurricane impact at this time.

As a reminder, I still feel that the MJO will make it more difficult for new storm formation between September 10th and 25th, so the peak of the season could be quiet for new development.