Hurricane Irma is now a Category 5 storm with sustained winds of 185 miles per hour and gusts exceeding 200 miles per hour. If a storm were to hit land with this sort of intensity, catastrophic damage would result. Of course, sometimes hurricanes form over the ocean and really don’t create any issues for anything besides ships and fish. But this might not be that kind of storm.
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. Third, experts, backyard enthusiasts, and people with no idea how to forecast are all weighing in. If there were 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.
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. Notice the wind history below as Irma has moved across the Atlantic.
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. This then moves onshore, destroying 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 2 feet of rain in its path. This can obviously create extensive freshwater 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’ll take a turn to the north. The precise timing of the turn is critical to how the United States is affected. If the turn occurs early enough, the storm could move along the coastline and not hit any 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 would be if the storm misses Florida and heads into the Gulf of Mexico before coming north. This would bring probably 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 that 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.
Follow Dave Epstein on Twitter @growingwisdom.