Ryan Truchelut

WeatherTiger

We are less than a day away from a Big Bend hurricane strike with only a handful of antecedents in local weather history. And unfortunately, Hurricane Michael is intensifying, just as predicted.

As of the 5 p.m. Tuesday NHC advisory, Hurricane Michael has officially reached Category 3 intensity on the Saffir-Simpson Hurricane Wind Scale with maximum sustained winds of 120 mph. With the eye clearing out and recon and satellite observations of a nearly closed eyewall, Michael may not be done strengthening and is as likely as not to reach Category 4 intensity in the next 12 hours.

Michael looks to peak in intensity overnight, just as it reaches the westward apogee of its arc across the Gulf of Mexico. Most hurricanes approaching the northern Gulf weaken somewhat on approach, but there continue to be reasons why Michael will defy that precedent.

There remains more warm water with depth that is typical in the northeastern Gulf, and the dry continental airmass that often wraps into eastern Gulf storms is unlikely to significantly disrupt the core prior to landfall.

This means limited or no weakening prior to reaching the coast. The NHC forecast of Category 3 landfall intensity remains the most likely case. Sustained winds can make quick jumps up or down, so you should not be overly invested in the exact landfall intensity.

Even if Michael were to weaken, there is no realistic scenario in which it will not be a powerful and destructive storm for the Big Bend.

If you followed our coverage Tuesday, you’ll recall that I laid odds on impact outcomes in Leon County proper along the lines of four historical storms: Irma, Hermine, Kate, and the Great Hurricane of 1851.

Michael's place in a history of hurricanes:Hurricane Michael will wreak havoc, may make Tallahassee history

The latest from the storm's path:

As Michael has proceeded straight down the NHC’s track forecast line, the cone has narrowed and the odds of the relatively less bad outcomes in Tallahassee (roughly analogous to the inland wind damage observed from Irma or Hermine) from a landfall west of Panama City Beach have declined to less than 5 percent and around 20-25 percent, respectively.

What is left is likely landfall on a swath of coastline between Panama City Beach and Apalachicola in the early afternoon hours Wednesday.

The National Weather Service provides a handy way to understand the severity of the four key risks posed by tropical cyclones, which is called the Hurricane Threats and Impacts product.

I’m going to walk you through each of those four HTI hazards and discuss their potential severity for Tallahassee and Apalachee Bay based on a landfall on either the west or east end of that likely range.

Threat 1: Wind

Wind impacts in Leon County remain a tricky forecast even 24 hours out. While any path east of Panama City will very likely bring wind gusts in the 75 to 95 mph range to Tallahassee Wednesday afternoon, a landfall point closer to Apalachicola would mean that at least a portion of the eyewall inner core of Michael would pass directly over Leon County.

With Michael plowing rapidly northeast, in that circumstance wind gusts in Tallahassee would likely exceed 100 mph sometime Wednesday afternoon.

Whether or not we get the core is the difference between Kate-level effects and the yet more severe effects akin to hurricanes in 1851 or 1894. With the single most likely landfall spot near Mexico Beach, in good agreement with a tight model consensus and the NHC track, Kate (or Kate-plus) wind effects remain the most likely outcome in Tallahassee, at around 50 percent odds.

Still, the 25 percent chance of at least a partial core strike on Tallahassee, and the concomitant increase in inland wind damage, cannot be ruled out at this stage.

Risk: Major (west track); extreme (east track).

Threat 2: Surge

In hurricanes, it’s water that kills.

The lens shape and shallow depth of Apalachee Bay will focus a massive flux of Gulf water driven by southerly winds to the east of the center into 9 to 13 feet of surge from Port St. Joe to Cedar Key for a track on the west end of the likely range, or 12- to- 15-feet values for a more eastern track. Note that these surge heights are significantly higher than the 6 to 9 feet observed in the Bay during Hurricane Dennis in 2005.

Simply put, you are putting your life at grave danger if you remain in a mandatory coastal evacuation area. If you’re reading this from a surge evacuation zone, stop reading and leave.

Risk: Extreme.

Threat 3: Flooding Rainfall

Expect 3 to 5 inches in Tallahassee with a west track and 5-10 inches with an east track. This could cause some flooding of low-lying inland areas, but unlike stalling storms events like Harvey and Florence, Michael will be rocketing northeast at more than 20 mph upon landfall, which should keep rainfall totals relatively in check.

Risk: Moderate.

Threat 4: Tornadoes

An isolated tornado or two is possible over the Big Bend associated with the outer bands of Michael, primarily overnight tonight. Overall, not a major concern.

Risk: Low.

At this point, with Tallahassee potentially on the eastern edge of the core, all there is left to do is watch the movement of the storm hour-by-hour and count each precious mile Michael moves west of north. Tallahassee weather should be fine into the overnight hours tonight, but you should be where you’re going to be until Thursday morning by daybreak Wednesday.

I’ll be back Wednesday morning with an overnight recap by 7 a.m., followed by a Hurricane Michael liveblog on tallahassee.com that will go until there is nothing left to say, or until technical difficulties mean I can post no more.

Keep watching the skies.

Dr. Ryan Truchelut is co-founder and chief meteorologist at WeatherTiger, which provides weather and climate forecast solutions for government and private enterprise. Get in touch at ryan@weathertiger.com. A more detailed version of WeatherTiger’s hurricane outlook, with additional animated GIFs, is free to read at weathertiger.com.