ATMO 9/18 Hurricanes

Hurricane Structure:
- Eye: calm area with few clouds ranging from 5-125 miles, averaging 20-40 miles
- Eye Wall: Most intense winds and clouds
- Core of Strong Winds: 50-300 miles

- Winds rise around the eye wall and sink in the center of the eye
- Low pressure in the center of the storm
- Warm core from condensation and cloud formation (warm from release of latent heat)
- Eye wall Replacement Cycle: the eye wall closes in on itself while weakening and then as it's replaced by an eye wall forming outside the collapsing one the storm will most likely strengthen
- Outer or Spiral Rain Bands
- Out flow of air at the top of the storm

Formation and Dissipation:
- We still don't know everything about hurricanes and intense amounts of research is being done to try to understand the storms

Requirements:
- Warm, Humid surface air and an unstable atmosphere
- Warm ocean surface waters (T > 80F, 26.5C) and a depth of warm water > 60 m or 200 ft
- Pre-existing large-scale surface convergence and/or upper-level divergence
- Must be 4 degrees of latitude away from the equator to have counter-clockwise rotating winds (from Coriolis force)
- Absence of strong vertical wind shear

Importance of No Vertical Wind Shear:
- Wind Shear: when winds change in speed and/or direction with increasing altitude
- Wind shear inhibits stacked convection and can "rip" tropical storms apart

Wind Shear Example:
- Wind speed increases as altitude increases (stronger winds as you go further up into the atmosphere)
- Spreads the latent heat over a larger area preventing a concentrated warm core

- The rate at which air pressure decreases with increasing altitude depends on air temperature in the vertical column of air. The warmer the air, the slower the rate of pressure decrease.

Steering Hurricanes:
- At any one time, the high pressure regions are separated into elongated cells. Breaks in cells allow storms to be steering away from the tropics
- Above 30 degrees latitude, storms pick up speed as the steering level winds become stronger
- The bermuda high plays a strong role in steering US land falling hurricanes

Forecasters Must Predict:
- Future storm position
- Future storm intensity (usually more difficult)
- Forecasts have gotten much more accurate but they are still round 100 miles off for 24 hour position forecasts

Hurricane Dangers:
- Strong winds
- Heavy rains
- Storm surges
- Tornados

Storm Surge:
- The rise in sea level along a coast as on shore winds pile up the water. More like a big dome of water rather than big waves. In the northern hemisphere, the greatest storm surge and strongest winds occur to the right of the storm center (with respect to the direction the storm is moving).

Winds:
- Counter-clockwise winds cause right-front side of the storm to have the on shore winds of say 100 mph, add in the speed the entire storm is moving (20 mph), the front-right quadrant has 120 mph winds. The front-left quadrant has offshore winds of 100 mph, subtract the speed the entire storm is moving (20 mph), the front-left quadrant has 80 mph winds.