Jeff Masters Hurricane Blog

Deaths from Ian pass 100; 91L looms » Yale Climate Connections


The death toll from Hurricane Ian’s rampage through Florida has risen to at least 101, and four more deaths in North Carolina bring its total U.S. death toll to 105, according to CNN. Ian at this point is the 6th-deadliest U.S. hurricane since 1980, according to statistics of direct and indirect hurricane deaths maintained by key federal agencies (Figure 1). Direct deaths include drowning in storm surge, storm-driven waves, rip currents, or freshwater flood from rain; falling trees are also a common source of direct deaths. Causes of the indirect deaths include falls during post-storm clean up, traffic accidents, carbon monoxide poisoning from generators, and medical issues compounded by a hurricane.

Figure 1. Hurricane Ian has the sixth-highest death tool (direct plus indirect deaths) of any hurricane since 1980, according to statistics from NOAA/NCEI.

Ian also killed three people in Cuba, and sank a boat near Stock Island in the Florida Keys carrying 27 Cuban migrants to Florida. Nine migrants on the boat were rescued, two were killed, and 16 are missing. The Coast Guard called off the search for the missing people on Monday.

According to a National Hurricane Center publication, the deadliest Florida hurricane prior to Ian was the catastrophic category 5 1935 Labor Day hurricane, which killed 408 people. Note, however, that the NHC catalogs only direct hurricane deaths in these statistics, and the cause of many of the 101 deaths reported in Florida from Ian has not been released. Drowning because of storm surge has been the dominant cause of death when a cause has been reported, though, so many of the 101 Florida deaths will likely end up being direct deaths.

Why so many deaths?

The primary reason for Ian’s high death toll is relatively straightforward: A large number of people in a vulnerable location subject to strong hurricanes leads to a high number of deaths. The amount of risky development that has occurred in southwest Florida – near sea level, on barrier islands, and on former wetlands – was a disaster waiting to happen, and it happened. Cape Coral, where some of Ian’s deaths were reported, was a particularly vulnerable location, because of unwise building practices (see Tweet below).

This highly vulnerable population had the added hazard of having to interpret a difficult forecast situation. Ian was approaching the coast at an oblique angle, so that small changes in the hurricane’s projected track made a large difference in where the storm would hit. Moreover, the forecast situation was more uncertain than usual, since the steering currents for Ian were relatively weak; Ian’s eventual landfall location was near the edge of the cone of uncertainty 48-72 hours before landfall.

Nevertheless, NHC made good forecasts in a difficult situation, and continually called attention to the more-than-usual forecast uncertainty. A storm surge watch was posted for the entire southwest coast of Florida all the way to the Everglades, including Ian’s eventual landfall location and the Naples area, at 11 p.m. Sunday, advising of a storm surge of 4 – 7 feet in and around the Fort Myers area. This watch was upgraded to a storm surge warning from Tampa south to the Everglades at 5 p.m. Monday, well before Ian’s 3 p.m. Wednesday landfall.

Climate change may also have contributed to the death toll. Part of the reason Ian caught people unprepared resulted from the hurricane’s rapid intensification shortly before landfall. In just three hours on Wednesday morning, Ian intensified by 35 mph, topping out as an extremely dangerous high-end category 4 hurricane with 155 mph winds. NHC’s intensity forecast was for Ian to be a low-end Cat 4 with 130 mph winds at landfall. Ian hit with 150 mph winds, which likely made it about three times more destructive than if it had hit with 130 mph winds.

As discussed here, a 2019 paper found that 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 research found that for the strongest 5% of storms (which includes Ian), 24-hour intensification rates in recent storms were about 10 mph higher than than they were 30 years earlier. Thus, climate change makes the most dangerous hurricanes – high-end storms like Ian that rapidly intensify just before landfall, potentially catching an unprepared population off guard – more likely.

Another was climate change acts as a threat multiplier for hurricanes: oceans warmed by climate change put more moisture in the atmosphere, leading to heavier hurricane rainfall (see Tweet above). Also, storm surges from landfalling hurricanes now are able to cause much more damage and more risk of fatalities, since human-caused sea level rise enables storm surges to push farther inland and cause deeper flooding. Two separate studies – a 2021 paper by scientists at Climate Central, and a 2014 study by Lloyds of London – found that sea-level rise over the past century near New York City led to far more extra storm surge damage during 2012’s Hurricane Sandy. Sea-level rise along the southwest Florida coast over the past 100 years has been about a foot, likely contributing to billions of dollars of extra storm surge damage from Ian.

Disturbance 91L poses threat to the Caribbean

A tropical wave designated Invest 91L was several hundred miles east of the Windward Islands on Tuesday, headed west at 15 mph. This system has the potential to develop into a named storm that could threaten parts of the Caribbean late this week.

91L had favorable conditions for development on Tuesday, with warm waters near 29 degrees Celsius (84°F), moderate wind shear of 10-20 knots, and a moist atmosphere (a mid-level relative humidity of 70%). Satellite imagery on Tuesday afternoon showed that 91L had developed a surface circulation center, fully exposed to view, well to the northwest of the disturbance’s heavy thunderstorms. This surface swirl had separated from 91L’s main blob of heavy thunderstorms because westerly winds were creating a moderate 10-20 knots of wind shear. Small swirls like this usually do not become full-fledged surface circulation centers around which a storm will coalesce – unless the storm’s heavy thunderstorms can build toward the swirl and draw it in. However, a Tuesday afternoon mission by an Air Force hurricane hunter aircraft showed a surface circulation center might be forming near the northwest edge of 91L’s heavy thunderstorms, and the 12Z Tuesday SHIPS model forecast predicted that wind shear over 91L would fall today, perhaps allowing a well-formed surface circulation to form.

91L will pass through the Windward Islands on Tuesday night and Wednesday morning, and enter the eastern Caribbean. Tuesday morning runs of the GFS and European ensemble model forecasts gave 91L more support for development than their Monday forecasts had indicated, with the operational version of both models now calling for a tropical storm to form in the central or southwestern Caribbean this weekend. A number of models show 91L eventually becoming a hurricane in the western Caribbean.

Figure 2. Track forecasts out to 10 days for 91L from the 12Z Tuesday, October 4, run of the GFS ensemble model. Individual forecasts of the 31 ensemble members are the lines color-coded by the wind speed in knots they predict for 91L; red colors correspond to a category 1 hurricane. The time in hours from the model initialization time are in grey text. The more southerly ensemble members were for a weaker storm; a more northerly track was indicated for a stronger storm. (Image credit: weathernerds.org)

The models have large differences in the forward speed of 91L, with the 0Z Tuesday European model predicting 91L will be at the coast of Nicaragua on Saturday night, and the 6Z Tuesday GFS model showing the system still in the central Caribbean at that time. A slower system will have more time to intensify and be a bigger threat; a faster moving storm is more likely to arrive in Central America as a weaker system. As 91L progresses westward across the southern Caribbean, it will bring heavy rains to the northern coast of South America and the ABC Islands, and it is possible that land interaction will inhibit development. The model runs available early Tuesday afternoon showed that 91L’s heavy rains would likely remain south of Puerto Rico, Hispaniola, and Jamaica.

A narrow ridge of high pressure to the north of 91L should keep it confined to the Caribbean, with Nicaragua and Honduras at most risk of seeing impacts by early next week. In its 2 p.m. EDT Tuesday Tropical Weather Outlook, NHC gave 91L 2-day and 5-day odds of development of 40% and 70%, respectively.

Figure 3. Visible image of Invest 92L at 1525Z (11:25 a.m. EDT) Tuesday, October 4, 2022. (Image credit: tropicaltidbits.com)

92L may be a short-lived tropical depression in the open Atlantic

Another disturbance, this one named Invest 92L and centered around 30 degrees west longitude in the eastern Atlantic, continued to gradually organize on Tuesday. Convection (showers and thunderstorms) around 92L was more expansive than on Monday, and one pocket of convection was located near a distinct area of mid-level rotation.

Conditions will remain supportive for 92L on Tuesday, amid light to moderate wind shear (5 to 15 knots), a moist mid-level atmosphere (relative humidity of 60-65 percent), and warm sea surface temperatures around 28 degrees Celsius (82 degrees Fahrenheit). From Wednesday to Friday, wind shear will ramp up markedly to 20 to 30 knots, likely capping off any development. Intensity models are of limited use for a system like 92L which has yet to close off a low-level center. The GFS and Euro ensemble models provide modest support for the idea of 92L’s becoming a tropical depression by Wednesday. It’s possible 92L could then hang on as a depression or a weak tropical storm into the weekend, when wind shear is predicted to ease, allowing the storm another chance to gain strength.

92L will move northwest for a couple of days before angling westward late this week as it encounters a blocking ridge of high pressure to its north. Models suggest the system will eventually recurve next week into the central Atlantic without threatening land areas. In its Tropical Weather Outlook issued at 2 p.m. EDT Tuesday, NHC gave 92L an 80% chance of developing into at least a depression in the next two days, with the same odds for the five-day period, suggesting that any development over the next five days would be expected to happen by Thursday).

The next two names on the Atlantic list of storms are Julia and Karl.

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