Early Hurricane Notes

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Early Hurricane Notes

• ATS 553

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Hurricane Classification

• TROPICAL WAVE
• A trough or cyclonic curvature maximum in the
  tradewinds

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Hurricane Classification

• TROPICAL DISTURBANCE
• A discrete system of apparently organized
  convection maintained for a day or more

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Hurricane Classification

• TROPICAL STORM
• A warm core tropical cyclone with closed isobars,
  rotary circulation, and winds between 34 and 64
  knots.
• WHEN THEY GET THEIR NAME

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Hurricane Classification

• HURRICANE/TYPHOON
• A warm core tropical cyclone with closed isobars,
  rotary circulation, and winds of at least 64
  knots.
• Does not necessarily have an eye, but often does.

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Characteristics
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Naming Hurricanes

• In the Atlantic
• A, B, C, D
• Alternate boy-girl
• Rotate through six lists
• Retire names for especially damaging storms

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Eastern Pacific

• Very similar scheme as in the Atlantic

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Western Pacific

• Just uses a long list
• In alphabetical order BY THE COUNTRY THAT
  SUBMITTED THE NAME
• Names can be retired, too.

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Other Basins

• Use other schemes
• Usually just short lists that they rotate through
  as needed

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Historically

• Prior to WWII, storms were named after the patron
  saint of the day.
• Post WWII, various schemes
• Phonetic alphabet (alpha, bravo, charlie..)
• Animals (Antelope, Bear, Cat, Dog)
• Adjectives (Aggressive, Blusterly)
• All Female Names starting in the mid 1950s
• Male names started in 1979

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Tropical Cyclones vs. Midlatitude Cyclones

• Strongest Winds
• MC Jet Stream
• TC Surface

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Tropical Cyclones vs. Midlatitude Cyclones

• Core Temperature
• MC Cold core (trough)
• TC Warm core (LHR in eyewall, subsidence in eye)

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Tropical Cyclones vs. Midlatitude Cyclones

• Structure
• MC Asymmetric, fronts
• TC Symmetric, no fronts

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Tropical Cyclones vs. Midlatitude Cyclones

• Scale
• MC Synoptic scale
• TC Mesoscale in size, synoptic scale in duration

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Why Winds Decrease With Height In A Hurricane

• ATS 553

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Warm Core Systems
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Temperature Gradient!
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From Above
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From Above
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From Above
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What if this were a regular warm front?

• What would the Thermal Wind relationship tell us
  about how winds would be changing with respect to
  height?

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What if this were a regular warm front?

• Wind speeds at the surface would be weak.
• Aloft, there would be a Midlatitude Jet Stream!

Winds would be getting more positive with height!
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What if this were a regular warm front?
Height
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Wind Speed
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But This Is NOT a Midlatitude Cyclone
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But This Is NOT a Midlatitude Cyclone
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Strong Surface Winds
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With height, these winds DECREASE due to the
Thermal Wind Relationship!
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Strong Surface Winds
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get weaker with height
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even reverse aloft..
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to create the upper-level anticyclone!
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Wind Profile
Height
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Wind Speed
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Hurricane Cookbook

• 1. High SSTs (at least 26C)
• Flux of sensible and latent heat
• Hurricanes do NOT seek out warm water

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Hurricane Cookbook

• 2. Coriolis Force (at least 5 off of the
  equator)
• Hurricanes are in CYCLOSTROPHIC balance, not
  GEOSTROPHIC BALANCE
• However, Coriolis Force keeps the winds from just
  following directly into the region of low
  pressure when it first forms.
• Hurricanes dont FORM at the equator.
• Hurricanes dont CROSS the equator!

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Hurricane Cookbook

• 3. Instability
• Rules out subtropical highs, which are regions of
  sinking motion and high stability
• KNOW WHY SINKING MOTION IS ASSOCIATED WITH
  INCREASED STABILITY!

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Hurricane Cookbook

• 4. No wind shear
• Redistributes vertical profile of latent heat
  release, setting up the wrong circulation
  patterns
• TUTTTropical Upper Tropospheric Trough

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TUTT June thru August
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Hurricane Cookbook

• 5. High relative humidities through midlevels of
  the troposphere
• Helps reduce the impact of entrainment.
• Individual Cumulus towers are easily destroyed by
  entrainment of dry air.

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Hurricane Cookbook

• 6. An initial disturbance
• Unorganized groups of thunderstorms organize into
  tropical storms.
• Typically these are West African Squall Lines or
  other disturbances in the AEJ.

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Saffir-Simpson Scale
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