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Meteorological phenomenon can span large ranges in size and strength and categorizations exist based on thresholds, One example is the Saffir–Simpson hurricane wind scale (SSHWS) (see also NOAA)

Tropical Depression TD11 (LUPIT) will be passing by and I saw an Extremely Heavy Rain Advisory with a color-coded map of counties in Taiwan categorized as

  • Heavy Rain (yellow)
  • Extremely Heavy Rain (orange)
  • Torrential Rain (red)
  • Extremely Torrential Rain (purple)

update: It's been pointed out that there is a "descriptions tab" on the page which says:

  • Heavy Rain: 24-hour accumulated rainfall exceeds 80 millimeters, or 1-hour rainfall exceeds 40 millimeters.
  • Extremely Heavy Rain: 24-hour accumulated rainfall exceeds 200 millimeters, or 3-hour accumulated rainfall exceeds 100 millimeters.
  • Torrential Rain: 24-hour accumulated rainfall exceeds 350 millimeters, or 3-hour accumulated rainfall exceeds 200 millimeters.
  • Extremely Torrential Rain: 24-hour accumulated rainfall exceeds 500 millimeters.

I'm curious if these four descriptions are standardized categories or are simply chosen here to give a sense of increasingness to the progression in color and severity of rainfall.

So I'd like to ask:

Are terms like "Extremely Torrential Rain" universal in meteorology? Are these standardized categories widely used in meteorology or are these ad hoc definitions for this weather service?


Screenshot from https://www.cwb.gov.tw/V8/E/P/Warning/W26.html circa 01:30 07-Aug-2021 UTC

Extremely Torrential Rain from https://www.cwb.gov.tw/V8/E/P/Warning/W26.html circa 01:30 07-Aug-2021 UTC

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  • $\begingroup$ Downvoted because the answer to your question is right there, in the link you provided. All you had to do to get an answer to your question was to click on the "Description" button, which contains "Extremely Torrential Rain: 24-hour accumulated rainfall exceeds 500 millimeters." $\endgroup$ Aug 7 at 8:41
  • $\begingroup$ @DavidHammen is that particular definition only used on that website or is it used in the greater meteorology community as well? One goal of Stack Exchange questions is to provide a space for good answers for the benefit of future readers. $\endgroup$
    – uhoh
    Aug 7 at 8:47
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    $\begingroup$ Then you should rephrase your question: Is this a definition used only in Taiwan, or does it have a wider acceptance? $\endgroup$ Aug 7 at 8:48
  • $\begingroup$ @DavidHammen how does that look? $\endgroup$
    – uhoh
    Aug 7 at 8:54

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