Jeff Masters Weather Blog

Hurricane Idalia hits Florida as a Cat 3 with 125 mph winds » Yale Climate Connections


Hurricane Idalia powered ashore in Florida’s Big Bend region at 7:45 a.m. EDT Aug. 30 as a Category 3 storm with 125 mph winds and a central pressure of 949 mb. Idalia is tied with the 1896 Cedar Key hurricane as the most powerful storm on record to strike Florida’s Big Bend. Idalia put on a very impressive burst of rapid intensification just before landfall, its winds increasing from 75 mph to 130 mph in the 24 hours ending at 5 a.m. EDT Wednesday. An eyewall replacement cycle kicked in just before Idalia hit the coast, weakening the winds by 5 mph.

A record storm surge

Idalia brought a record storm surge to two of the three tide gauges with long periods of record along the most affected coastline. At Cedar Key, located about 55 miles to the southeast of where the hurricane’s eye came ashore, a peak storm surge of 8.91 feet was observed, and the highest water level was 6.89 feet above high tide (Mean Higher High Water, or MHHW). In records extending back to 1914, this was the highest water level ever observed there. The previous record was 5.98 feet above MHHW, set in 2016 during Hurricane Hermine. Idalia’s peak surge arrived shortly after low tide — water levels would have been over two feet higher had the storm hit at high tide.

In Tampa Bay, a storm surge of four to five feet caused extensive flooding and was one of the highest storm surges there since the 1921 hurricane. Near downtown Tampa, Idalia’s storm surge at the East Bay tide gauge peaked at 5.69 feet; this surge arrived at mid-tide, and the highest water level was 4.56 feet above high tide (MHHW). This is considered moderate flooding. This station does not have a long-term period of record.

At the St. Petersburg tide gauge, also located in Tampa Bay, water levels peaked at 3.82 feet above MHHW. This was the second-highest on record, behind the 4 feet observed in 1985 during Hurricane Elena. Records extend back to 1947 at the site.

At the Clearwater Beach tide gauge, on the Gulf of Mexico side of St. Petersburg, a storm surge of about 5.3 feet was observed, and water levels peaked at 4.05 feet above MHHW. This was the highest on record, beating the 4.02 feet observed in 1993 during the “Storm of the Century.” Records extend back to 1973 at the site.

Sparse wind data from Idalia

Although Idalia was born from a broad circulation, it ended up being on the small side as a hurricane. At 5 a.m. EDT, several hours before landfall, when Idalia was at peak Category 4 strength, NOAA estimated that sustained hurricane-force winds (74 mph or stronger) covered a circle 30-35 miles wide. Peak winds typically diminish quickly as a hurricane moves onshore — one of several reasons why it can be difficult to confirm sustained hurricane-force winds at landfall, as we covered in detail in a two-part 2018 write-up. At the same time, people often underestimate the damage a given wind speed can produce.

Read: Hotter ocean temperatures from global warming likely increased Idalia’s destructive power by at least 40-50% 

The sparse population and limited observing network of the Florida Big Bend will likely make the task of confirming Idalia’s hurricane-strength winds tougher than usual. Below are some initial wind reports Wednesday morning, collected at the standard height of 10 meters (33 feet):

  • NWS/Perry, Florida (western eyewall): 62 mph gusting to 85 mph at 8:15 a.m. EDT
  • NWS/Tallahassee, Florida (western side of core): 30 mph gusting to 46 at 8:53 a.m. EDT
  • Florida Coastal Monitoring Program tower near Hampton Springs: gust to 81 mph
  • Moody Air Force Base, Georgia: 43 mph gusting to 56 mph
  • Brucell Junction, Florida: 85 mph gust
  • Horseshoe Beach, Florida: 81 mph gust
  • Keaton Beach, Florida: 77 mph gust
  • Mayo, Florida: 73 mph gust

Forecast for Idalia

Idalia will remain a potent wind- and rain-maker as it moves northeastward from the Florida Panhandle very close to the coasts of Georgia and South Carolina into Wednesday night. By Thursday morning, Idalia is predicted to be angling eastward and out to sea from just off the coast of North Carolina. Idalia is predicted to diminish below hurricane strength by Wednesday night, but it is predicted to remain at moderate tropical-storm strength until it moves offshore. As a result, Idalia could produce gale-force sustained winds of 50 to 60 mph — enough to bring down trees and power lines — throughout its trek across the Southeast U.S., from the coast to 50 miles or more inland and from Georgia to parts of North Carolina. As of 1 p.m. EDT, over 375,000 customers in the Southeast U.S. were without power.

The heaviest rains from Idalia will fall in a strip along and just west of Idalia’s center, extending across the coastal plains of Georgia and the Carolinas where widespread rains of two to six inches and local totals of six to 10 inches or more are predicted. Soils are relatively moist over much of the area, and the NOAA/NWS Weather Prediction Center is calling for a moderate risk of flood-producing excessive rains along and near Idalia’s path.

High pressure will be building into the northwest Atlantic in the wake of powerful Hurricane Franklin (see below), and this will tend to keep Idalia looping in a clockwise fashion for several days, eventually heading southeastward by Friday into the weekend. What happens at that point remains highly uncertain. The European and GFS forecast ensembles show wide disagreement on Idalia’s track beyond 72 hours, including some possibility it will loop southward toward lower latitudes early next week. The official National Hurricane Center forecast as of 11 a.m. Wednesday predicts that Idalia will instead angle back to the east-northeast by Sunday, perhaps passing near Bermuda. Strong wind shear (20 to 35 knots) and dry air aloft are expected to prevail during Idalia’s foray this weekend across the Northwest Atlantic, which would keep it a tropical storm at best despite very warm sea surface temperatures.

Figure 1. Track forecasts out to five days for Idalia from the 06Z Wednesday, Aug. 30, 2023, run of the European ensemble model (left) and GFS ensemble model (right). Individual forecasts of the 51 Euro and 31 GFS ensemble members are the lines color-coded by the wind speed in knots they predict for Idalia; red colors correspond to a Category 1 hurricane. The time in hours from the model initialization time is in gray text. Long-range models such as the European and GFS models are less reliable guides to storm intensity than higher-resolution, shorter-range models such as HWRF, HMON, and HAFS. (Image credit: weathernerds.org)

A record battering: Nine major hurricane U.S. landfalls in the past seven years

Idalia’s landfall gives the U.S. nine major Atlantic hurricane landfalls in the past seven years (2017-2023), eight of them being continental U.S. landfalls. This ties 1915-1921 and 1944-1950 for most continental U.S. major hurricane landfalls in a seven-year period. The nine total major hurricane landfalls (including Hurricane Maria in Puerto Rico) are a record for any seven-year period. Remarkably, the U.S. had no major hurricane landfalls during the 11-year period 2006-2016 (after getting seven during the two-year period 2004-2005).

The other major hurricane landfalls during the past seven years include one other Category 3 storm (Zeta of 2020 in Louisiana), plus seven Category 4 and 5 storms: Harvey (2017 in Texas), Irma (2017 in Florida), Maria (2017 in Puerto Rico), Michael (2018 in Florida), Laura (2020 in Louisiana), Ida (2021 in Louisiana), and Ian (2022 in Florida). That’s as many Cat 4 and 5 landfalls as occurred in the prior 56 years (Charley, 2004; Andrew, 1992; Hugo, 1989; Celia, 1970; Camille, 1969; Betsy, 1965; and Carla, 1961). The only comparable beating the U.S. has taken from Category 4 and 5 landfalling hurricanes occurred in the six years from 1945 to 1950, when five Category 4 hurricanes hit South Florida. And Idalia came very close to making a Category 4 landfall.

Idalia one of a recent record number of rapidly intensifying storms at landfall

Idalia is one of just 10 historical storms since 1950 that have rapidly intensified by at least 40 mph in the 24 hours before landfall (using data from the regular six-hourly fix just before landfall, data from the actual landfall point, or in the case of Hurricane King of 1950, the point one hour after landfall). It is sobering to see that five of those storms, below in boldface, occurred in the past seven years:

Humberto, 2007 (65 mph increase)
Ida 2021 (60 mph increase)
King 1950 (60 mph increase)
Idalia 2023 (45 mph increase)
Laura 2020 (45 mph increase)
Michael 2018 (45 mph increase)
Harvey 2017 (40 mph increase)

Cindy 2005 (40 mph increase)
Danny 1997 (40 mph increase)
Eloise 1975 (40 mph increase)

As discussed in detail in our 2020 post, rapidly intensifying hurricanes like Idalia, Ida, Michael, Laura, and Harvey that strengthen just before landfall are among the most dangerous storms as they can catch forecasters and populations off guard, risking inadequate evacuation efforts and large casualties. Unfortunately, not only is human-caused climate change making the strongest hurricanes stronger, but it is also making dangerous rapidly intensifying hurricanes like Idalia more common.

According to research published in 2019 in Nature Communications, “Recent increases in tropical cyclone intensification rates,” Atlantic hurricanes showed “highly unusual” upward trends in rapid intensification during the period 1982–2009, trends that can be explained only by including human-caused climate change as a contributing cause. The largest change occurred in the strongest 5% of storms: For those, 24-hour intensification rates increased by about 3-4 mph per decade between 1982 and 2009.

Figure 2. Satellite image of (left to right) Hurricane Franklin, the remnants of Tropical Storm Gert, and Tropical Depression 11 at 1530Z (11:30 a.m. EDT) Wednesday, Aug. 30, 2023. (Image credit: RAMMB/CIRA/CSU)

Elsewhere in the Atlantic

Idalia wasn’t the only major hurricane in the Atlantic on Wednesday. Hurricane Franklin was still at Category 3 strength as Idalia surged to Category 3 strength, both packing top sustained winds at 115 mph as of 2 a.m. EDT Wednesday. The overlap was brief, as Franklin had weakened below major-hurricane strength by 5 a.m., but it still marked the first time in 73 years that the Atlantic had two major hurricanes at the same time during any August. (Category 3 begins at 111 mph.)

Franklin peaked at 150-mph sustained winds late Monday, making it the most powerful Atlantic hurricane ever observed so far north in the open Atlantic (not including the Gulf of Mexico). As of 11 a.m. Wednesday, Franklin was still angling past Bermuda, located about 160 miles northwest of the island, and heading northeast at 13 mph with top sustained winds of 105 mph. Winds on Bermuda were mostly below tropical-storm-force strength except at elevation. Franklin will continue gradually weakening but should remain at hurricane strength for at least two or three more days as it continues northeast into the open North Atlantic. There are three other systems of note in the Atlantic:

  • Tropical Depression 11 continues to drift atop the unusually warm waters of the subtropical Atlantic well southeast of Bermuda. Showers and thunderstorms (convection) continue to pulse near TD 11, but strong wind shear and a dry atmosphere have kept TD 11 below tropical storm strength, and the depression is predicted to become a remnant low by Thursday night.
  • Just southwest of TD 11, the long-lived remnants of former Tropical Storm Gert continue to spawn scattered convection. The 2 p.m. EDT Wednesday Tropical Weather Outlook from the National Hurricane Center gave the system only a 10 percent chance of development, primarily over the next couple of days.
  • A tropical wave designated as Invest 94L near the Cabo Verde Islands has a better chance of development: 50 and 60% over the next 2- and 5-day periods, respectively. Light wind shear (5-10 knots), a moist midlevel atmosphere (relative humidity around 70%), and warm sea surface temperatures of 27-28 degrees Celsius (81-82 degrees Fahrenheit) may allow 94L to become a tropical depression or tropical storm as soon as Thursday or Friday. The next name on the Atlantic list is Jose.

Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.





Source link