Generally speaking, but not always, the lower the atmospheric pressure within a storm, the stronger the winds and greater amount of precipitation it can produce.
Synoptic conditions near the low-pressure area and topography on the land are also crucial in determining winds, rain and snowfall.
The standard pressure reading at sea level is about 1,013.25 millibars, abbreviated mb, or 29.92 inches of mercury, rendered as inHg.
The Labor Day hurricane of 1935 that slammed into the Florida Keys had the lowest measured surface pressure ever recorded in North America, reaching an incredible 892 mb or 26.35 inHg.
To look at it from another perspective, you would have to climb a 3,500-foot mountain to reach the same pressure as was experienced in this hurricane at sea level.
Sustained winds were estimated to have reached 200 mph. It was reported that survivors saw the sky fill with sparks, perhaps from small rocks striking each other in the extreme winds.
For many years, scientists believed that this was the limit or cap for hurricane intensity. Then in October 1979, Typhoon Tip in the Western Pacific reached 870 mb or 25.69 inHg.
A few years ago, Hurricane Patricia tracked along Mexico’s western coast with sustained winds of 213 mph and gusts estimated well over 225 mph.
Patricia reached the lowest atmospheric pressure ever recorded in the Western Hemisphere, an awe-inspiring 879 mb or 25.96 inHg at the ocean’s surface in October 2015.
Unofficially, Typhoon Haiyan may have hit 860 mb or 25.40 inHg at its peak on Nov. 7, 2013, just before making landfall on Samar island in the Philippines. If that is ever officially verified, it would be the lowest sea-level pressure ever recorded.
Just last week, Typhoon Hagibis off the east coast of Japan hit 900 mb or 26.58 inHg.
It’s interesting to note the cyclone will move northeastward and become extratropical as it journeys to the Aleutian Islands early this week.
Looking forward, will hurricanes become more intense due to global warming? Because an accurate record of hurricane pressure readings is limited, it’s a highly complicated question.
However, according to Yale Climate Connections, “The conventional wisdom is that storm intensity will increase, but storm frequency will either decrease or remain unchanged.”
I agree with that hypothesis, and here’s why:
A warmer atmosphere can hold more water vapor. For every 1 degree Fahrenheit increase in temperature, the air can hold around 4% more water vapor.
As the atmosphere and oceans continue to warm, cyclones, on average, have been producing heavier rainfall events, according to the hard-working scientists and researchers at Climate Central.
The eyewall of a hurricane is its engine, and warm seawater is its fuel. For the storms to strengthen, the seawater temperatures must be at least 80 degrees Fahrenheit or higher.
The warmer the ocean and the air above it, the more evaporation that can occur, which increases relative humidity/water vapor levels.
Tropical cyclones derive most of their energy from the release of “latent heat,” when enormous amounts of water vapor from the ocean’s surface are condensed into liquid water, which is a warming process. You may have noticed that it gets warmer right before it rains.
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Physically, tropical cyclones have their strongest winds near the Earth’s surface and don’t have fronts — warm, occluded or cold — associated with them. Hurricanes weaken when they lose touch with the hot water that fuels them.
“Tropical cyclones” is the generic term for an organized system of convective clouds that rotate around an area of low pressure over tropical or subtropical waters.
In the Northwest Pacific, it’s called a “typhoon,” and “cyclones” happen in the South Pacific and the Indian Ocean.
Remember, doubling the wind speed does not double its force upon an object, like a house, but quadruples it. A Category 5 hurricane is 500 times stronger than a Category 1.
Also, rising sea levels are making cyclones more destructive due to higher storm surges.
That leads to the question: Is there some way to prevent the genesis of a hurricane? Or if one does develop, is there a way to change its course or weaken it?
At this point, it’s much more cost-effective to reduce greenhouse gas emissions or relocate homes and businesses to areas that don’t have a high vulnerability to such storms.
Nevertheless, over the years the U.S. government, scientists and engineers have worked on technologies to reduce the threat.
One idea is utilizing wave energy to drive pumps on surface barges or ships that would bring cold water from the ocean depths to the surface in hopes of decreasing sea surface temperatures below 80 degrees in the hurricane’s path to sap its strength.
Another idea along those lines was to tow icebergs from the Arctic into the track of a cyclone.
The U.S. government program called “Stormfury” tried to weaken hurricanes by using cloud seeding with silver iodide flares mounted on aircraft, but it had very little success and has since been abandoned.
Another idea was the coat the ocean with a Jell-O-like substance or gigantic-size rolls of plastic wrap to reduce evaporation from the ocean’s surface.
One scheme that has been proposed since the late 1950s was to explode a hydrogen bomb in the eye of the hurricane, which probably wouldn’t do anything except to create a radioactive cyclone.
By the way, the first person to name tropical cyclones was Clement Lindley Wragge of Queensland, Australia, in the late 1800s.
Wragge had an inclement temper, and he took to naming cyclones after politicians whom he disliked.
A forecaster could publicly describe a storm named after a politician as “wandering about the ocean with no aim or purpose.”
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I will give two presentations about climate change and what it means for our local weather Tuesday, Oct. 15. The first presentation will be from 3:30 to 5 p.m. at the Atascadero Library, 6555 Capistrano Ave., Atascadero.
Then I will also be giving a talk for the Estero Bay CERT group at 6:30 p.m. at the Morro Bay Fire Department, 715 Harbor St., Morro Bay. All are welcome, including families.