We should use central pressure deficit, not wind speed, to predict hurricane damage

Posted: November 8, 2017 by oldbrew in atmosphere, methodology, predictions, wind

Hurricane Katrina, 2005 – The air pressure, another indicator of hurricane strength, at the center of this Category 5 storm measured 902 millibars, the fourth lowest air pressure on record for an Atlantic storm. The lower the air pressure, the more powerful the storm.
[image credit: Jeff Schmaltz, NASA/GSFC]

This is supported by Hurricanes – Science and Society, which says:
‘It is well accepted that the most influential factor in storm surge generation is the central pressure deficit, which controls the intensity of a hurricane, i.e. wind velocity and stress over the ocean surface and inverse barometric effects.’

The system for categorizing hurricanes accounts only for peak wind speeds, but research published in Nature Communications explains why central pressure deficit is a better indicator of economic damage
from storms in the United States, reports Phys.org.

“Sandy is the classic example. It was a very big storm, but in terms of maximum wind speed it was arguably not a hurricane,” said Dan Chavas, an assistant professor of atmospheric science at Purdue University who led the study. “If you looked at the central pressure deficit, you would have expected it to cause a lot of damage. But if you used maximum wind speed, as people usually do, you wouldn’t expect it to do the damage that it did.”

Central pressure deficit refers to the difference in pressure between the center of the storm and outside it. Pressure and wind speed have been used interchangeably to estimate potential damage from hurricanes for years, but the relationship between them has been a long-standing riddle in tropical meteorology.

Chavas and his colleagues have defined a theory that solves that riddle. Previous work has observed that central pressure deficit depends on maximum wind speed, storm size, and latitude, but Chavas’ team has determined why that is.

Scientists could use this theory to calculate peak wind speed if they had numbers for the other metrics in the equation, which could come in handy because wind speeds need to be measured at several points of a storm, making it difficult to get an accurate reading.
The research team tested their theory on two simulations of Earth.

The first used the actual distribution of sea surface temperatures and solar radiation since 1979 to produce conditions similar to real historical climate.

The second simulation produced a very simplified version of the Earth. It had no land, and ocean temperature and solar radiation were the same everywhere. This made the entire planet sort of like the tropics, meaning hurricanes could pop up anywhere – but they still tended to form at low latitudes and move westward and toward the poles, like they do on Earth.

Continued here.

More information: Daniel R. Chavas et al,
Physical understanding of the tropical cyclone windpressure relationship, Nature Communications
(2017). DOI: 10.1038/s41467-017-01546-9

  1. oldbrew says:

    Sandy briefly re-intensified to Category 2 intensity on the morning of October 29, around which time it had a wind diameter of over 1,150 miles (1,850 km), and a central pressure of 943 mb, which set records for many cities across the Northeastern United States for the lowest pressures ever observed. [bold added]


  2. oldbrew says:

    List of Atlantic hurricane records

    Several lists using different data types. Older hurricanes less accurately measured, or even not measured at all?

  3. craigm350 says:

    OB – There are that many uncertainties with past records that it’s hard to compare with our current sampling. Although from 2005/6 this article gives a good flavor of the uncertainties throughout all the ocean basins;


  4. oldbrew says:

    They touted 2005 as some kind of ‘new normal’ for hurricane seasons, but that idea failed pretty comprehensively.
    = = =
    And now…

    Here comes La Niña, El Niño’s flip side, but it will be weak
    November 9, 2017

    The National Oceanic and Atmospheric Administration said Thursday, Nov. 9, 2017 that a weak La Nina has formed and is expected to stick around for several months.

    Read more at: http://phys.org/news/2017-11-la-nina-el-nino-flip.html
    – – –
    During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5 °C. In the United States, an appearance of La Niña persists for at least five months. It has extensive effects on the weather in North America, even affecting the Atlantic and Pacific hurricane seasons.

    – – –
    BOM Australia: All international climate models suggest further cooling of the tropical Pacific is likely, with most models reaching La Niña thresholds in late 2017. Six of eight models suggest that these levels will persist long enough to be considered an event. If La Niña does develop, it is likely to be weak and short-lived.


  5. tom0mason says:

    Surely a figure that reflects the central pressure deficit over the area (or volume) of the air mass would be a more useful number for hurricane intensity.

  6. oldbrew says:

    Tom – the report says ‘Central pressure deficit refers to the difference in pressure between the center of the storm and outside it.’

    If you use the whole air mass it wouldn’t be ‘central’?
    = = =

    Date: 09/11/17 USA Today


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