Hurricane Irma, is now a Category 5 storm with sustained winds of 185 mph and gusts exceeding 200 mph. If a storm were to hit land with this sort of intensity, catastrophic damage would result. Hurricanes, of course, form over the ocean and, unless they reach land, really don’t create any issues for anything besides ships and fish. This storm is now at the highest intensity category for a hurricane.  There is no Category 6.

Life-threatening Type Of Storm

Irma is getting a tremendous amount of attention for several reasons. First, it’s a very dangerous storm. If this hurricane hits land, we are looking at more human suffering on a widespread scale. Second, after Harvey, everyone is aware of worst-case scenarios. They usually don’t happen, but they can. Irma, coming so close on the heels of Harvey, is generating a tremendous amount of coverage. Get used to it. The coverage isn’t going to end soon. Third, in a world of massive social media information, actual experts, backyard enthusiasts and people with no idea how to forecast, everybody is weighing in on Irma.  If there was a category for hype, we are rapidly approaching a Category 5.

Make no mistake, the threat to the islands of the Lesser Antilles, Haiti, the Dominican Republic, Cuba and the United States is real. However, there are still many unknowns. Computer models aren’t perfect.

As this storm moves westward and then eventually turns north, a difference in track of 50 miles can mean someone’s house is wiped off its concrete slab versus losing a few shingles. The most intense winds from this storm are highly concentrated near the eye of the storm. Notice the wind history below as Irma has moved across the Atlantic.

Hurricane force winds only are found about 50 miles from the center of the storm in all directions.  (NHC)

Rainfall and storm surge

Most of the deaths from these storms occur from water, not wind. The storm will push a wall of water, known as the storm surge, along its path. As the storm approaches an area, the strong wind and pressure differences around the storm create a bubble of water sometimes 10 or 15 feet high, which then moves onshore and destroys many buildings along the way.

This storm won’t bring 4 feet of rain as did Harvey, because it won’t stall. However, there still could be 1 to two 2 of rain in it’s path. This can obviously create extensive fresh water flooding.

Threat to the United States and New England

We know Irma is going to continue in a general westward movement the rest of the week.  We also know eventually it takes a turn to the north. The precise timing of the turn is critical to how the U.S. is impacted. If the turn occurs early enough, the storm could move along the coastline and not hit land. If the change in direction occurs just south of Florida, the storm could move through that state and then head north along the coast affecting multiple regions, even New England. The storm would weaken dramatically along the way, but still create issues here sometime late next week.

Less likely, the storm misses Florida and heads into the Gulf of Mexico before coming north. This would bring likely bring a major hurricane of wind and rain to the Gulf Coast, but no major issues for New England.

Upper Pattern Evolution

There are three major players in the forecasting game we need to watch.  There are two highs and a trough all vying for control of the steering wheel of Irma. Alone, the forecasting puzzle would be easier, but when you have all three and each changes hour to hour, it makes this more challenging. That’s one of the reasons there is less confidence beyond this weekend. There will be several changes to the track of the storm in the days ahead. A path over the mountains of Hispaniola and Cuba would weaken the storm, a path which stayed over water and then hit Florida would be the worst-case scenario, let’s hope we only have one worst-case storm this season and it already happened.

The evolution of the upper pattern in the coming days will determine the track of Irma

Follow Dave Epstein on Twitter @growingwisdom