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Tropical cyclone rainfall climatology
From Wikipedia, the free encyclopedia
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| Tropical cyclones |
| Formation and naming |
|---|
| Development - Structure Naming - Seasonal lists - Full list |
| Effects |
|
Effects |
| Climatology and tracking |
| Basins - RSMCs - TCWCs - Scales Observation - Rainfall forecasting - Rainfall climatology |
One of the most significant threats from tropical cyclones is heavy rainfall. Large, slow moving, and non-sheared tropical cyclones produce the heaviest rains. The intensity of a tropical cyclone appears to have little bearing on its potential for rainfall over land, but satellite measurements over the last several years show that more intense tropical cyclones produce noticeably more rainfall over water. Flooding from tropical cyclones remains a significant cause of fatalities, particularly in low-lying areas. During the 2005 season, flooding related to Hurricane Stan's broad circulation led to 1662-2000 deaths.
- See also: Tropical cyclone rainfall forecasting
While flooding is common to tropical cyclones near a landmass, there are a few factors which lead to excessive rainfall from tropical cyclones. Slow motion, as was seen during Hurricane Danny (1997) and Hurricane Wilma, can lead to high amounts. The presence of topography near the coast, as is the case across much of Mexico, Haiti, the Dominican Republic, much of Central America, Madagascar, Réunion, China, and Japan acts to magnify amounts due to upslope flow into the mountains. Strong upper level forcing from a trough moving through the Westerlies, as was the case during Hurricane Floyd, can lead to high amounts even from systems moving at an average forward motion. Larger tropical cyclones tend to drop more rainfall as they precipitate upon one spot for a longer time frame than average or small systems would. A combination of two of these factors could be especially crippling, as was seen during Hurricane Mitch in Central America.[1]
| Rainfall Rate per day within radius of the center (Riehl) | |||
|---|---|---|---|
| Radius (mi) | Radius (km) | Amount (in) | Amount (mm) |
| 35 | 56 | 33.98 | 863 |
| 70 | 112 | 13.27 | 337 |
| 140 | 224 | 4.25 | 108 |
| 280 | 448 | 1.18 | 30 |
Isaac Cline underwent the first investigations into rainfall distribution around tropical cyclones in the early 1900s. He found that a larger proportion of rainfall typically falls in advance of the center (or eye) than after the center's passage, with the highest percentage falling in the right front quadrant. Father Viñes of Cuba found that some tropical cyclones can have their highest rainfall rates in the rear quadrant within a training (non-moving) inflow band (Tannehill 1942). Rainfall is found to be strongest in their inner core, with a degree of the center, with lesser amounts farther away from the center (Riehl 1954). Most of the rainfall in hurricanes is concentrated within its radius of gale-force winds.[2] The chart to the right was developed by Riehl in 1954 using meteorological equations which assume a gale radius of about 140 statute miles, a fairly symmetric cyclone, and does not consider topographic effects or vertical wind shear. As seen in the statistics from Taiwan/Taipei below, local amounts can exceed this chart by a factor of two due to topography. Wind shear tends to lessen the amounts below what is shown on the table.
Larger tropical cyclones have larger rain shields, which can lead to higher rainfall amounts farther from the cyclone's center.[2] This is generally due to the longer time frame rainfall falls at any one spot in a larger system, as long as forward motion is similar to that of a smaller system. Some of the difference seen concerning rainfall between larger and small storms could be the increased sampling of rainfall within a larger tropical cyclone when compared to that of a compact cyclone; in other words, the difference could be the result of a statistical problem.
Storms which have moved slowly, or loop, over a succession of days lead to the highest rainfall amounts for several countries. Riehl calculated that 33.97 inches/863 mm of rainfall per day can be expected within one-half degree, or 35 miles/56 km, of the center of a mature tropical cyclone. Many tropical cyclones progress at a forward motion of 10 knots, which would limit the duration of this excessive rainfall to around one-quarter of a day, which would yield about 8.50 inches/216 mm of rainfall. This would be true over water, within 100 miles/160 km of the coastline,[3] and outside topographic features. As a cyclone moves farther inland and is cut off from its supply of warmth and moisture (the ocean), rainfall amounts from tropical cyclones and their remains decrease quickly.[4]
Vertical wind shear forces the rainfall pattern around a tropical cyclone to become highly asymmetric, with most of the precipitation falling to the left and downwind of the shear vector, or downshear left. In other words, southwesterly shear forces the bulk of the rainfall north-northeast of the center.[5] If the wind shear is strong enough, the bulk of the rainfall will move away from the center leading to what is known as an exposed circulation center. When this occurs, the potential magnitude of rainfall with the tropical cyclone will be significantly reduced.
As a tropical cyclone interacts with an upper-level trough and the related surface front, a distinct northern area of precipitation is seen along the front ahead of the axis of the upper level trough. This type of interaction can lead to the appearance of the heaviest rainfall falling along and to the left of the tropical cyclone track, with the precipitation streaking hundreds of miles or kilometers downwind from the tropical cyclone.[6]
Between 1970-2004, inland flooding from tropical cyclones caused a majority of the fatalities in the United States.[7] This statistic changed in 2005, when Hurricane Katrina's impact alone shifted the most deadly aspect of tropical cyclones back to storm surge, which has historically been the most deadly aspect of strong tropical cyclones.[8] On average, five tropical cyclones of at least tropical depression strength lead to rainfall across the contiguous United States annually, contributing around a quarter of the annual rainfall to the southeast United States. While many of these storms form in the Atlantic Basin, some systems or their remnants move through Mexico from the Eastern Pacific Basin. The average storm total rainfall for a tropical cyclone impacting the lower 48 from the Atlantic Basin is about 16 inches/406 mm, with 70-75 percent of the storm total falling within a 24 hour period. The highest point total was seen during Amelia 1978, when 48 inches/1218 mm fell upon central Texas.[9]
- China tropical cyclone rainfall climatology
- Extratropical cyclone
- List of wettest tropical cyclones by country
- Tropical cyclone
- Tropical cyclone rainfall forecasting
- Tropical cyclogenesis
- United States tropical cyclone rainfall climatology
- Ivan Ray Tannehill. Hurricanes. Princeton University Press: Princeton, 1942.
- Herbert Riehl. Tropical Meteorology. McGraw-Hill Book Company, Inc.: New York, 1954.
- Terry Tucker. Beware the Hurricane! Hamilton Press: Bermuda, 1966.
- ^ Are You Ready?. Federal Emergency Management Agency (2006-04-05). Retrieved on June 24, 2006.
- ^ a b Corene J. Matyas. Relating Tropical Cyclone Rainfall Patterns to Storm Size. Retrieved on 2007-02-14.
- ^ Russell Pfost. Tropical Cyclone Quantitative Precipitation Forecasting. Retrieved on 2007-02-25.
- ^ David Roth. Tropical cyclone rainfall maxima by state. Retrieved on 2007-03-21.
- ^ Shuyi S. Chen, John A. Knaff, and Frank D. Marks, Jr. Effects of Vertical Wind Shear and Storm Motion on Tropical Cyclone Rainfall Assymetries Deduced from TRMM. Retrieved on 2007-03-28.
- ^ Norman. W. Junker. Hurricanes and extreme rainfall. Retrieved on 2006-02-13.
- ^ Ed Rappaport. Inland Flooding. National Oceanic & Atmospheric Administration. Retrieved on June 24, 2006.
- ^ Eric S. Blake; Jerry D. Jarrell, Edward N. Rappaport, Christopher W. Landsea. The Deadliest, Costliest, and Most Intense United States Tropical Cyclones From 1851 to 2004. National Oceanic & Atmospheric Administration. Retrieved on June 24, 2006.
- ^ David Roth. Tropical Cyclone Maxima. Retrieved on 2007-03-28.
- Individual Tropical Cyclone Rainfall Pages for the United States and Mexico
- Individual Tropical Cyclone Rainfall Pages for Puerto Rico/U.S. Virgin Islands
- Maximum amounts in the lower 48 United States by state
- Typhoon Rainfall Statistics and Forecasting (China)
- Deadliest, Costliest, and Most Intense United States Tropical Cyclones From 1851 to 2004
- Are You Ready? Hurricanes