tc impacts 7

Tropical Cyclone Impacts: 

Tropical Cyclone Impacts

Outline: 

Outline Wind Saffir-Simpson scale Storm Surge SLOSH Tornadoes Rainfall

Wind: 

Wind Caused by pressure gradient force The Saffir-Simpson Scale provides a classification system for TCs Developed by Herb Saffir Adopted by Bob Simpson (NHC director, 1969) Robert Simpson

Wind Damage by Category: 

Wind Damage by Category Category 1 Unanchored mobile homes, shrubbery, small trees, coastal flooding Category 2 Roofing, door, window damage, considerable tree damage Category 3 Structural damage to small buildings, trees blown down, mobile homes destroyed

Wind Damage by Category: 

Wind Damage by Category Category 4 Total roof failures, extensive damage to all buildings Category 5 Complete roof failures on many buildings, some buildings completely destroyed

Storm Surge: 

Storm Surge Rise in sea level due to “piling up” of water by wind and a small rise due to vacuum suction by storm’s low pressure Does not include waves on top of surge Range from inches to over 10 meters (30+ ft.) Height depends on: strength of wind field, extent of wind field, speed of storm, coastline shape, slope of continental shelf

Sample Storm Surges: 

Sample Storm Surges Galveston, 1900 (6,000+ fatalities)

Bhola Cyclone (1970): 

Bhola Cyclone (1970) 500,000 + (?) drowned in the early morning hours 20 ft. storm surge 120 mph winds http://upload.wikimedia.org/wikipedia/en/8/89/1111700858.JPG

Modeling Storm Surge: 

Modeling Storm Surge Sea, Lake and Overland Surges from Hurricanes (SLOSH) Run at the NHC Predictors Storm size Storm pressure Forward speed Track Wind speed and extent Coastline features Accurate within 20% of actual surge values Highly dependant on track forecast

Tornadoes: 

Tornadoes Gentry (1983) study (1960-1982 hurricanes): Nearly every hurricane spawned tornadoes during landfall 60% of tropical storms produced a tornado Virtually all tornadoes occurred in right front quadrant Most are weak (some up to F-3 strength) 80% formed in outer rainbands, 20% near outer eyewall

Slide16: 

Locations of tornado formation relative to storm heading (1973-1980) From Gentry (1983)

Tornado Formation in a TC: 

Tornado Formation in a TC Strong vertical shear of horizontal wind sets up in right front quadrant Land enhanced friction Strong updraft tilts vortex vertically

Tornado Formation in a TC: 

Tornado Formation in a TC Preferred formation time between noon and 6 pm Atmosphere most unstable, tilting most likely Tornadoes associated with hurricanes and time of day (From Gentry 1983, Copyright American Meteorological Society

Rainfall: 

Rainfall Can be devastating, even in weaker TCs Correlation between rainfall intensity and storm strength (Cerveny and Newman 2000)

Rainfall Distribution: 

Rainfall Distribution Inner core of TCs produce about 25% of the total rainfall for the system Higher for weaker systems (>30%) and Category-5 systems (~35%) Rainfall higher for storms that are deeper in the tropics Weakening as storms move over cooler SSTs

Slide21: 

From Cerveny and Newman (2000)

Slide22: 

Houston, TX after Tropical Storm Allison (2001)