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Early Hurricane Notes. ATS 553. Hurricane Classification. TROPICAL WAVE: A trough or cyclonic curvature maximum in the tradewinds. Hurricane Classification. TROPICAL DISTURBANCE: A discrete system of apparently organized convection maintained for a day or more. Hurricane Classification.
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Early Hurricane Notes ATS 553
Hurricane Classification • TROPICAL WAVE: • A trough or cyclonic curvature maximum in the tradewinds
Hurricane Classification • TROPICAL DISTURBANCE: • A discrete system of apparently organized convection maintained for a day or more
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”
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.
Naming Hurricanes • In the Atlantic: • A, B, C, D… • Alternate boy-girl • Rotate through six lists • Retire names for especially damaging storms
Eastern Pacific • Very similar scheme as in the Atlantic
Western Pacific • Just uses a long list • In alphabetical order BY THE COUNTRY THAT SUBMITTED THE NAME • Names can be retired, too.
Other Basins • Use other schemes • Usually just short lists that they rotate through as needed
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
Tropical Cyclones vs. Midlatitude Cyclones • Strongest Winds: • MC: Jet Stream • TC: Surface
Tropical Cyclones vs. Midlatitude Cyclones • Core Temperature: • MC: Cold core (trough) • TC: Warm core (LHR in eyewall, subsidence in eye)
Tropical Cyclones vs. Midlatitude Cyclones • Structure: • MC: Asymmetric, fronts • TC: Symmetric, no fronts
Tropical Cyclones vs. Midlatitude Cyclones • Scale: • MC: Synoptic scale • TC: Mesoscale in size, synoptic scale in duration
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?
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!
What if this were a regular warm front? Height 0 Wind Speed
With height, these winds DECREASE due to the Thermal Wind Relationship!
Wind Profile: Height 0 Wind Speed
Hurricane Cookbook • 1. High SSTs (at least 26°C) • Flux of sensible and latent heat • Hurricanes do NOT “seek out” warm water
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 don’t FORM at the equator. • Hurricanes don’t CROSS the equator!
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!
Hurricane Cookbook • 4. No wind shear • Redistributes vertical profile of latent heat release, setting up the wrong circulation patterns • TUTT—Tropical Upper Tropospheric Trough
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.
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.
