GEOL 106 Lecture Notes - Lecture 39: Extratropical Cyclone, Landfall, Northern Hemisphere
26 May 2018
School
Course
Professor
- geographic regions at risk for hurricanes and tropical storms:
o entire Gulf Coast from southern Texas to southern Florida and Atlantic Coast from
southern Florida northward through coastal provinces of Canada
o hurricane strike probabilities are particularly high along coasts of southern Florida,
Alabama, Mississippi, Louisiana, eastern Texas, Cape Hatteras
o greatest hurricane threat in southeastern US, threat to New England often
underestimated
▪ e.g. Great Hurricane of 1938, struck Long Island without warning and killed 680
people in New York, Connecticut, Massachusetts
▪ 2012 Hurricane Sandy, largest hurricane on record
- north America is not the most hazardous:
o northwest Pacific generally ha 3X the number of hurricanes as North Atlantic
o Pacific and Indian Oceans overall have more hurricanes
o South Atlantic and southeast Pacific rarely have hurricanes because of their cold surface
waters
o hurricanes do not form close to equator because of absence of Coriolis effect and once
formed, do not cross the equator
- hurricanes affecting North America:
o generally develop in summer and early fall
o length of hurricane season varying from year to year
o official Atlantic season: June 1 and ends Nov 30
o most Atlantic hurricanes occur in August, September, October when sea surface is
warmest
o season for tropical cyclones in Southern Hemisphere is from Jan to April
- in NA: geographic region at risk from extratropical cyclones is far larger than from tropical cyclones
o severe weather from extratropical cyclones is greatest in interior of continent but may
also occur in coastal areas
o greatest threat for this severe weather varies with location and time of year
o in winter months, extratropical cyclones create strong windstorms along Pacific Coast and
nor’easters on Atlantic Coast as well as produce heavy snowstorms and blizzards
especially in Sierra Nevada Mountains and within east of Rocky Mountains
o during spring and summer: extratropical cyclones are responsible for severe
thunderstorms and tornado hazards in US and Canada east of Rocky Mountains
10.4 Effects of Cyclones
- both types of cyclones produce:
o flooding, thunderstorms, tornadoes
o extratropical cyclones: snowstorms, blizzards
- 3 additional effects of cyclones that are especially damaging:
o storm surge, high winds, heavy rains
o in hurricanes: storm surge causes greatest damage and contributes to 90% of human
fatalities in hurricane
STORM SURGE
- storm surge: local rise of sea level that results primarily from water that is pushed toward shore by
winds that swirl around a storm
- major hurricanes, intense extratropical cyclones on coastline generate storm surges of more than 3m
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Both types of cyclones produce: flooding, thunderstorms, tornadoes: extratropical cyclones: snowstorms, blizzards. 3 additional effects of cyclones that are especially damaging: storm surge, high winds, heavy rains in hurricanes: storm surge causes greatest damage and contributes to 90% of human fatalities in hurricane. Storm surge storm surge: local rise of sea level that results primarily from water that is pushed toward shore by winds that swirl around a storm. Most hurricanes in northern hemisphere: storm surge is greatest in right forward quadrant of storm as it makes landfall. Height of storm surge is greatest near tie of maximum wind speed and is greater if landfall takes fastest in right forward (front) quadrant place at high tide. Washover channels: these features that are problematic when they cut entirely through islands or peninsulas and isolate one area form another: most are naturally repaired by coastal currents and wave action in months after storm.
