weather, weather safety/preparedness

Dangerous Irma Targeting Naples (H. Michael Mogil, CCM, CBM, NWA-DS*)

As of late yesterday afternoon, downtown Naples, U.S. Highway 41 (Tamiami Trail), and Naples/Collier County beaches resembled a ghost town. One could drive down Gulfshore Boulevard (a thoroughfare about a block or so from the beach) and perhaps see one or two cars. Fig. 1 shows the scene sans vehicles.

It was eerie.

But there was good cause for the lack of humankind. After a week of Hurricane Irma track uncertainty across the state of Florida (the large-scale storm track was “spot on;” the details across Florida, not so), computer and human thinking centered on a track along the west coast of Florida. Now, early Saturday morning (Sept. 9, 2017), the expected storm track is actually slightly west of Naples (i.e., with the center remaining over water). This is reminiscent of Donna (which destroyed the Naples Pier in 1960) and Charley (which slammed into Punta Gorda, north of Fort Myers in 2004).

This sets the stage for a worst-case scenario for Collier and Lee Counties.

Specifically,

high winds – much of Collier and Lee Counties will be impacted by triple digit sustained winds because the eye wall will be passing directly over both counties. Wind gusts can easily reach speeds that are 20 percent higher than sustained winds. Even though Irma has weakened slightly this morning (due in part to interaction with topography across Cuba), reintensification is expected later today (once Irma leaves Cuba).

heavy rainfall – since the right side (i.e., the wet side) of the storm will be affecting the two counties, roughly eight to 12 inches of rainfall (with locally higher amounts) is anticipated. Given recent heavy rainfall and flooding, these two-day rainfall totals may help replicate the recent flooding.

tornadoes – again the right side of the storm (mainly, the leading front right quadrant) is where tornadoes are most likely to form. That storm quadrant will be passing directly over Collier and Lee counties during the day on Sunday. Fortunately, most hurricane-generated tornadoes are weak and short-lived.

storm surge – is not an instantaneous (or wall-like) rise of water. Rather, it is the relentless onslaught of waves pushing water onshore, without the corresponding opportunity for water to flow back to the ocean. As a result, water levels can rise and push far inland.

Clearly storm surge will be a major risk for many areas. With a storm center over land, Naples and Fort Myers would not receive as much of an initial surge; with a storm offshore, an initial surge from the south is likely. Under either scenario, as the storm moves north of Collier and Lee Counties, hurricane force westerly winds will push additional salt water onto land areas for a longer period of time. Expected surge values will be in the six to 12 feet range.

High tides can add to the expected storm surge. Unfortunately, the turn to westerly winds will be occurring near the time of high tide (about 4:00p.m. E.D.T. on Sunday). Note that expected surge height values do not include any waves that may occur during the time of the storm surge.

Large areas of Collier County (and lesser areas in Lee and other west coast counties) are in the high surge flood risk. The map in Fig. 2 shows at surge risk areas due to a CAT 2 hurricane. Generally speaking the highest risk areas are south and west of State Highway 41.

This is a very large and very dangerous hurricane, one that can cause extensive damage to structures, trees, power lines and signs.

Since it’s too late to evacuate the area, it’s best for local residents and visitors to take shelter in sturdy structures or county-operated storm shelters. People living in mobile homes or manufactured housing should definitely leave these well in advance of the hurricane’s arrival.

© 2017 H. Michael Mogil

Originally posted 9/9/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.