Everything You Need To Know About Hurricane Irma

We continue to have a very complex forecast on our hands with Hurricane Irma, and while we do have some time to nail down the forecast, it’s understandable that residents along the East Coast and even along the eastern Gulf of Mexico are wanting to know what plans they should be making in preparation for Irma. Tonight’s article will not be particularly long and detailed, but I do briefly want to point out few things.

As of 8 pm ET, Hurricane Irma is a category 4 hurricane with sustained winds of 120 mph. Irma’s movement is finally back to the west after losing some latitude due to the influence of an upper-level low to the northeast of the system. Bermuda ridging should strengthen in the coming days to the north of Irma and could even build southwest, which will keep system generally on a westward track. Regions, across the northern Lesser Antilles and the Greater Antilles, including Puerto Rico, Haiti, Dominican Republic, and Cuba need to prepare to be impacted by a major hurricane. I have included the National Hurricane Center’s latest five-day forecast, and residents in those regions need to understand that a track just slightly farther to the south will worsen the possible impact from this storm. This could be a serious situation, so again, I urge residents of those islands to not take this threat lightly.

Figure 1: The National Hurricane Center’s latest 5-Day forecast for Irma (as of 8 pm ET)

Unlike with Harvey when it first made landfall, Irma’s forecast is quite complex due to the angle that it will be coming towards the coast of the contiguous United States, which could result in a level of uncertainty remaining even by the end of the week or weekend. Additional complicating factors to this forecast include numerous features that will potentially be influencing the track of Irma, which will ultimately determine whether or not this system makes landfall in the U.S. In order to keep this forecast briefer than my last discussion, I’m going to provide a bullet-point list below. I will be providing a follow-up forecast either tomorrow night or Wednesday, depending on how things evolve over the next 18 to 24 hours.

Figure 2: Irma will continue moving westward into warm waters. The black dot represents Irma’s location as of 8 pm ET.

• First and foremost, residents across the entire coast of Florida and along the East Coast need to start making some preliminary plans, just in case. In particular, I urge residents from the southern Florida coastline to the Carolina coast to begin making plans and to continue following the forecasts closely. I still can’t rule out this system making it into the far eastern Gulf of Mexico; however, it still remains unlikely. Residents along the western Gulf of Mexico coast do NOT need to worry at this time. If a U.S. landfall occurs, it likely won’t occur until this weekend, at the earliest!
• A western ridge/eastern trough configuration is going to set up across the United States. If this pattern were to hold, this would allow Irma to safely recurve out to sea away from the U.S. However, this pattern is likely not going to hold long enough. The western ridge is probably going to break (imagine a wave crashing in the ocean), and while the trough could become cut-off from the main flow, it appears that it will move out to the northeast before Irma gets far enough northwest to be picked up. Ridging to the west will remain in place while Bermuda ridging will either build westward or remain in place. Between these two features, a weakness will still be present over the eastern U.S, which will eventually result in Irma taking a sharp turn to the north. The timing of this turn to the north will be everything. It will be the difference between this system going into the far eastward Gulf, through Florida, or impacting regions along the eastern coast of Florida and the Carolinas.
• Again, this forecast is tricky also because of the angle Irma will be coming in relative to the United States. With Harvey, it moved mostly perpendicular to the coast towards Texas before making its first landfall, so we knew that somewhere along the Texas coast was going to be heavily impacted by hurricane-force winds. In Irma’s case, it will be coming in parallel to the coastline or if it starts making its northward turn south of Florida, it could come in perpendicular to the south Florida coastline (but remember, the southern Florida coastline is MUCH shorter in length than the Texas coastline).
• At this point, I’m still not ruling out Irma only skirting the coastline or completely being a miss; however, that isn’t the most likely scenario. At this point, the most likely scenario is an impact to Florida, Georgia, and the Carolinas. Keep in mind that modifications to this forecast are likely, and that forecast confidence is much lower than usual.

Hopefully by Wednesday, we’ll get a much clearer picture of what could unfold. Just hang with us, and we’ll make sure we nail down this forecast for you as quickly as possible.