Hurricanes
•	Tropical cyclone
–	Need sustained winds of 75 mph, and ‘rotary circulation’ (has to if it is a cyclone…)
–	Called typhoons in Pacific, Willy-Willys in Australia
–	Start off as tropical depression
•	Depression? Low pressure
–	Then get to tropical storm stage (>37 mph winds
–	Finally hurricane (only few out of storms)

•	Make one?
–	Similar to mid latitude cyclone only in tropics
•	Latent heat powered as vapor condenses, promoting more uplift
•	Need warm waters to develop over (thus most from in late summer)
•	Form between 5o and 20o N/S
–	Why no higher?  Water not warm enough
–	Why no lower?  No Coriolis
•	Like we had Gulf of AK low form off cold Siberia, tropical storms can form off hot African Sahel

•	Sahel in trade winds, move storms westward
–	Trades; uniform, constant winds
–	To develop hurricane need Easterly Wave
•	‘kink’ in winds; bunching up causing convergence…thus lifting (if optimal? unstable conditions w/ divergence aloft)

•	Once formed (in Atlantic) move west in Trade winds
–	And slung by Bermuda/Azores high
•	So, it tracks across Atlantic and goes toward Gulf of Mexico, into coast, or up along coast
–	Notice that they stay strong all along coast…why?   Gulf Stream!
•	So, how do you kill a hurricane?
–	Run it into land (can’t get more power from latent heat, too dry)
–	Run it into cold water (see above)
–	Eliminate divergence aloft (collapse)