Hurricane Idalia: experts call out storm surge and inland wind risks

Hurricane Idalia will deliver storm surge threats along the Florida Gulf coast and wind threats inland after landfall as the storm system bears down on the Big Bend of the Florida Gulf coast as a major hurricane, industry experts are saying of the pending storm impacts.

Storm surge is of particular concern along the right hand side of the storm track, including the Tampa Bay area, as the major drive of likely damage. Inland wind damage towards the Florida capital of Tallahassee is also a concern. Landfall is currently called for a low population density region of the big bend stretch of the Florida Gulf coast.

At 2:00 AM US eastern time, the storm remained 100 miles (175 km) SW of Cedar Key Florida, traveling nearly due north at 15 mph (24 km/h). Maximum sustained wind speeds were listed at 120 mph (195 km/h).

Following are call out comments on physical risks from industry experts.

Andrew Siffert, SVP and senior meteorologist at BMS: “Idalia still looks to be a life-threatening storm with some mild impacts on the insurance industry. Some models bring it ashore as a Category 4. Others are Category 3, which is more likely at this time. As also highlighted, the Florida Gulf Coast's Big Bend region is extremely surge-vulnerable with likely up to 8-12 feet of inundation.

“High Ocean Heat Content values and upper atmospheric dynamics ... will promote storm strengthening and likely a period of rapid intensification. The only variable that will limit intensity is time before landfall, faster forward motion, and the potential for dry air to be entrained into Idalia as it grows into size.

“Time and time again, we have seen that water is the true killer in a hurricane, and no hazard is more deadly or destructive than a storm surge. .. the most damaging storm surge is not where the hurricane makes landfall, but it can be far removed down the storm's right side. ...An ill-timed full moon on Wednesday will further enhance tides and flood potential. Minor coastal flooding could occur in the Tampa Bay areas.

“Hurricane forecast winds … will surely be capable of knocking out power. ... wind speed and its destructive capabilities will depend on the building components. A major hurricane with such severe wind speeds has not tested this part of Florida's building stock.

“Tallahassee impacts are likely the wildcards in the overall insurance industry loss projection at this time.”

Jon Schneyer, director of catastrophe response at CoreLogic: “Life- and property-threatening coastal flooding from storm surge along the west coast of Florida is possible. Storm systems that make landfall along the Gulf Coast are likely to generate a more substantial storm surge than equivalent storms that hit the Atlantic Coast. This fact combined with Idalia’s angle of approach relative to the Florida coastline makes the threat of a devastating surge possible.

“CoreLogic® estimates approximately 808,321 single- and multifamily residential properties with $238.4 billion in combined reconstruction cost value (RCV) are at risk of storm surge flooding along the west coast of Florida. The largest number of at-risk homes are located in three Florida counties: Lee County, Pinellas County and Sarasota County" [in the Tampa Bay area at the southern tip of the hurricane warning zone].

Michael Lowry, meteorologist at the NHC's Storm Surge Unit: “While forecast guidance has settled on Idalia’s primary impact area in the Big Bend – from Crystal River to the south and east to Apalachicola in the west – the hurricane will have a long arm, especially to its south and east, where life-threatening storm surge is forecast hundreds of miles east of where Idalia washes ashore.

“Though the worst weather from Idalia will be near and well east of the center, those to the west – including inland cities like Perry, Crawfordville, and Tallahassee – shouldn’t sleep on this one. Coastal hurricane warnings extend westward to near Cape San Blas west of Apalachicola, with inland hurricane watches in place as far west as Leon and Wakulla Counties. High winds could cause widespread power outages well inland. Subtle adjustments west to the forecast may be necessary today if trends continue.”

Guy Carpenter - live event insights, Storm surge: “A significant storm surge is expected”: “A storm surge warning is in effect along portions of Florida’s Gulf Coast including Tampa Bay and the Big Bend Region. An inundation of 8 to 12 feet is possible along and to the right of landfall, which has the potential to severely impact structures and infrastructure, including rendering roadways impassable and destroying bridges. Based on the current NHC forecast, the largest storm surge is expected between Chassahowitzka and the Aucilla River. This includes the communities of Crystal River, Cedar Key and Steinhatchee.

“The Big Bend Region of the Florida Gulf Coast is particularly prone to large storm surges due to the depth and shape of the underwater terrain (bathymetry). The West Florida Shelf is a wide and very shallow ledge that extends nearly 200 miles off the Gulf Coast, which allows water to effectively pile up as hurricane winds drag water toward the shore. The geometry of the Big Bend coastline also allows water to funnel into the region from both the north and south.

“Wind: Idalia should bring major hurricane wind conditions to the Florida Big Bend Region and adjacent inland areas. Modest wind damage can be expected for affected structures meeting more recent building codes, with more substantial damage for older or less-resilient structures. Impacts will extend well away from the center of circulation to affect much of the Florida Peninsula, with the most severe effects along and to the right of the track. Tropical storm wind impacts will likely affect portions of Georgia and the Carolinas. Downed trees and powerlines can be expected over a widespread area.”

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