Dominating weather headlines ever since its creation, Irma has already created a swath of destruction in the Lesser Antilles.  Currently a Category 5 Hurricane, with sustained winds up to 175mph, Irma shows no signs of slowing down.  This has put coastal states such as Georgia, the Carolina’s, and especially Florida into a State of Emergency.

Forecast Track

Irma is currently North of the Dominican Republic and Haiti, tracking West-Northwest at 16mph.  Its direction will not change until late Friday into Saturday, when it begins to track North towards Florida.  When that turn will happen is still not certain.  An earlier turn would force Irma along the east coast, potentially lessening the impacts across the state of Florida.  But then there is the opposite.  If the turn is made later, the Florida Keys and South Florida would take a direct hit.

Forecast track for Irma as of 2pm Thursday, this track is subject to change as the National Hurricane Center periodically updates their forecast.

From a forecasting perspective, the setup is complex at best.  Interactions between the hurricane and an upper level low can have multiple outcomes, such as acting as a sling-shot directly inland to Georgia, and could also act to steer the storm further into the Carolina’s.  With that being said, a direct impact to the United States is gaining increasing confidence.

Intensity

The duration of Irma’s Category 5 status is one of historic proportions, and this intensity is not expected to change anytime soon.  Overall strength will likely fluctuate, but only slightly, as the storm undergoes sporadic eyewall replacement cycles.  Overall, the lack of features such as shear, dry air, or mountains disrupting the flow, meaning the hurricane is like a raging wildfire, with only more dry brush ahead of it.

“There are no obvious reasons why Irma will not remain a powerful hurricane for the next 3 days while approaching Florida. Thereafter, an increase in the wind shear could lead to gradual weakening, but Irma is expected to remain a major hurricane until landfall occurs.” Dr. Lexion Avila, Senior Hurricane Specialist, National Hurricane Center

One way the storm could weaken before impacting the US would be a direct hit to Cuba before the northern turn.  Cuba’s mountains are tall enough to weaken the core of the storm, but this outcome can essentially be ruled out.  The bottom line is that a major hurricane will impact the United States.

Impacts

While a majority of the impacts depend on Irma’s track, a few are more certain.   A Storm Surge Watch has been issued along the Southern Florida coast, with the primary concern along the southern and eastern edge.  Another area where surge is actually more likely is along the coast of Georgia and South Carolina.  The expansive wind-field of Irma will continue to push seawater over the Atlantic coast northward, making the probability of receiving over three feet of surge highly possible.

A graphic released by NWS Miami/South-Florida today, detailing the threats across their forecast area as Irma approaches.

Life-threatening winds will first take aim at Florida and the Keys, with gusts above 100 mph expected.  Even if the storm moves directly over Florida, it may weaken slightly, but its general circulation and intensity will stay intact until reaching further north.  It is still too early to tell how strong the winds will reach into Georgia. But the certainty is growing for widespread damage as well.

” The threat for major impacts to South Florida continues to increase. Destructive winds and life-threatening storm surge are the primary threats. Additional threats include flooding rains, isolated tornadoes, significant beach erosion and surf, coastal flooding, and life-threatening rip currents.” National Weather Service, Miami-South Florida Office

Heavy rainfall inland is expected with a tropical system of this size.  Up to 10 inches has been forecasted along the Atlantic Coast.  A  stream of winds onshore on the eastern side will serve to feed copious amounts of moisture and rainfall into the region.

Preparations

Evacuations have already been issued for the Florida Keys and across regions of South Florida, with more expected as the certainty of the track grows.  Home improvement and grocery stores have seen their own “storm surge” in the form of residents stocking up supplies to prepare for the worst, while hoping for the best.  The best way to prepare for a hurricane of this strength is to listen to local official and law enforcement, along with the National Hurricane Center and your local National Weather Service forecast office.

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About Kevin Thiel

Kevin is a Meteorology Major and Mathematics Minor at Ohio University, with an interest for thunderstorm electrification and research. On campus, he serves as President of the AMS Student Chapter, along with Webmaster and Forecaster for the campus atmospheric lab. This past summer, Kevin interned at the National Weather Service office in Miami, Florida, using lightning and radar data to study severe thunderstorm potential. One day, Kevin hopes to enter into field of academia and research, or become a forecaster with the Storm Prediction Center.
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