1 SourcesSources n AWS/TR-95/001 n AWS TR240 n NAVEDTRA 40970/40971 n JTWC Forecasters Handbook n NEPRF TR n Tropical Weather Course (Keesler) n Tropical TIPS

2 Tropical Cyclones

3 Bad Weather Vortices l Tropical cyclones – Tropical depressions - Winds < 34 knots – Tropical Storms - Winds knots – Hurricanes & Typhoons - Winds > 63 knots – Super Hurricanes & Typhoons - Winds – > 129 knots

4 Tropical Cyclones

5 General ClimatologyGeneral Climatology Life CycleLife Cycle StructureStructure WeatherWeather

6 Tropical Cyclones

7 Tropical Cyclogenesis l Seasonal Climatology – General u Latitude – No formation within 5° of equator – Genesis favored 5 to 15° – In Southern Hemisphere, no development poleward of 22°S – In Northern Hemisphere, development can occur up to 35°N

8 Tropical Cyclogenesis l Favorable conditions for development u Latitude: No formation within 5° of equator; need sufficient coriolis parameter to induce rotation - tropical cyclones are not purely cyclostrophic (i.e. like tornadoes). u Need energy source (High SST): As discussed before, ALL tropical convection is fed by the latent heat of condensation associated with rising moist air. Tropical cyclones are no exception. This latent heat comes from warm sea surface temperatures (SST’s) - minimum degrees F, through a 200 foot deep vertical ocean surface layer. Obviously, if a storm is over land, it looses energy.

9 Tropical Cyclogenesis l Favorable conditions for development u Need minimum wind shear: Strong wind shears tears CBs/TSTMs apart. Also, low wind shear allows the latent heat of condensation assocd with convective clouds to concentrate in an area, vs. spread out. Typically, 25 knots of wind will shear a tropical system. Also, storms that come under the influence of the jet stream(s) will be ripped apart (But be careful! The surface circulation can re-develop as an intense EXTRAPTROPICAL cyclone!) u Need Upper-level Divergent winds: This is needed to help “pump” the rising air away. Otherwise, the ideal convective cell won’t develop.

10 Tropical Cyclogenesis l Favorable conditions (con’t) u Need a Pre-existing Circulation: Tropical cyclones don’t come from “out of the blue”. They are relatively conservative features. There should be some kind of surface disturbance (such as a sfc trough, monsoonal trough, convergent winds at the surface, etc.). u Need Conditional Instability: Arguably, this is related to the point made above. The key point is that the Atmosphere must permit upward vertical motion. If the atmosphere is stable, CB’s won’t develop.

11 Tropical Cyclogenesis l Seasonal Climatology – General u Longitude: 90°E, 140°E, and 105°W are favorable u Majority form in summer (NW Pacific has them all year) u No development in South Atlantic or SE Pacific (too much shear)

17 Tropical Cyclone Life Cycle l Formative (Tropical Depression) Stage – Tropical Depression: winds 33 kts or less l Intensification stage-( Tropical storm / hurricane ) – Tropical storms have winds knots – Hurricanes have winds above 63 knots l Mature stage – Intensity changes little, kinetic energy at a maximum – Eye most clearly defined l Decaying Stage – Storm loses its source of latent and sensible heat

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19 Tropical Cyclone Life Cycle

20 From Demaria, 1998

21 From Demaria, 1998

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23 Tropical Cyclone Structure

24 Tropical Cyclone Structure

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26 Tropical Cyclone Structure

27 Tropical Cyclone Structure

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35 Tropical Cyclone Weather l Precipitation – Reaches a maximum over oceans in the right rear quadrant – Reaches a maximum after landfall in the right front quadrant l Tornadoes – Most likely near time of landfall due to strong shearing l Storm surge – Storm surge is responsible for most of the deaths along the coast.