Why awful Otis intensified so fast

Otis rapidly intensified to a Cat 5 hurricane last night CREDIT: National Oceanic Atmospheric Administration

You may have heard the term ‘rapid intensification’ before, and recently. For instance, Hurricane Idalia this year rapidly intensified with a wind increase of 55mph in 24 hours before striking northern Florida and last year Hurricane Ian did the same thing going from 115mph to 160mph in 24 hours before landing in Ft. Myers. The strict definition for hurricane rapid intensification is a wind strength increase of 35mph in less than 24 hours. In the Pacific, 2015′s Hurricane Patricia grew from 85mph to a whopping 205mph (peaking at 215mph), then weakened but still struck Mexico with 150mph winds. Otis surpassed that yesterday.

At 10am yesterday, Otis was STILL only a tropical storm with 70mph winds. By 1pm, a Cat 1 hurricane at 80mph. By 2pm, 110mph Cat 2. Then at 4pm, Otis strengthened to 125mph and by 7pm went to 145mph. Shortly before 10pm, the storm reached 160mph winds and 165mph by 11pm. And then, from the National Hurricane Center:

Satellite imagery indicates that Otis has made landfall near Acapulco, Mexico around 125 AM CDT (0625 UTC). The maximum sustained winds are estimated to be 165 mph (270 km/h), and the minimum central pressure is estimated at 923 mb (27.26 inches). Otis is a category 5 hurricane on the Saffir-Simpson Hurricane Wind Scale.

The reasons for this rapid intensification are pretty basic: a small storm over warm water with plenty of ventilation. Look at the 30°Celsius (86°F) water that Otis went over yesterday and keep in mind you only need 80° to supply the fuel for a hurricane:

CREDIT: Tropical Tidbits

That’s plenty of fuel. In addition, the storm was small and small storms tend either to strengthen or fall apart quickly. Almost like thunderstorms around here--they can build from a small sea breeze storm into a big cluster or just fall apart when they hit dry air. It all depends on the fuel. In this case, it was the latter--the fuel was there for Otis and while some dry air was present to the west, it wasn’t enough to keep the storm from growing.

In fact, an area of low pressure to the west supplied that dry air, but also supplied upper-level winds which ‘vent’ the storm. In other words, when air at the top of the storm is moved away by those westerly winds, then air at the bottom of the storm moves up to the top. If you take your hand and push water at the top of the swimming pool, water from below fills in pretty quickly. Why is this important to OTIS? Because when that air rises quickly from the bottom of the storm to the top, it cools rapidly and releases energy, thus intensifying.

Trough of low pressure vents the storm CREDIT: NOAA

As far as comparisons, Otis intensified by 85mph in only 12hours compared to Patricia’s 75mph in less than 12hours and set that new record. Likely many more have been broken. Of course, that matters little to the victims of this storm. They didn’t have a lot of time to prepare for a situation of this magnitude and the mudslides, surge and wind have taken a huge toll as we’ll continue to see in the days ahead. Prayers for our neighbors to the south.


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About the Author:

KPRC 2's chief meteorologist with four decades of experience forecasting Houston's weather.