AOSC 200Lesson 15

Fig. 8-18, p. 223

Computer generated image of Hurricane Mitch – October 26, 1998. Near

Honduras

Note the distinct ‘eye’ and the large extent of the hurricane

Fig. 8-19, p. 224

Damage from hurricane Andrew, August 1992

Fig. 8-23, p. 228

TROPICAL CYLONES• THESE INTENSE TROPICAL STORMS ARE KNOWN

BY DIFFERENT NAMES IN VARIOUS PARTS OF THE GLOBE:

• HURRICANES - ATLANTIC• TYPHOONS - WESTERN PACIFIC• CYCLONES - INDIAN OCEAN•• MOST FORM BETWEEN THE LATITUDES OF 5 TO

20 DEGREES.• LESS THAN 5 DEGREES, THE CORIOLIS FORCE IS

TOO SMALL• MORE THAN 20 DEGREES, THE TEMPERATURE OF

THE OCEAN IS TOO COLD• MUST HAVE WIND SPEEDS OF MORE THAN 119 KM

PER HOUR AND HAVE A ROTARY CIRCULATION TO BE A HURRICANE/TYPHOON

TROPICAL CYCLONE FORMATION• HURRICANES DEVELOP MOST OFTEN WHEN

OCEAN WATERS HAVE REACHED MAXIMUM TEMPERATURES - 25 C OR HIGHER.

• INITIAL STAGE IS SOME FORM OF DISTURBANCE - NAMED BY THE WEATHER SERVICE AS TROPICAL DISTURBANCES.

• ONLY A FEW TROPICAL DISTURBANCES DEVELOP 119 KM PER HOUR WINDS

• IF WINDS <119 BUT > 61 - TROPICAL STORM

• NAMES GIVEN WHEN STORM REACHES TROPICAL STORM STATUS

TROPICAL CYCLONES

• MATURE TROPICAL CYCLONES AVERAGE ABOUT 600 KM ACROSS

• BAROMETRIC PRESSURE CAN DROP ACROSS CYCLONE FROM 1010 TO 950 MILLIBARS

• THIS GENERATES RAPID, INWARD SPIRALING WINDS.

• AS AIR MOVES CLOSER TO CENTER ITS VELOCITY INCREASES

• CONSERVATION OF ANGULAR MOMENTUM.• IN THE CENTER OF THE EYE THE AIR IS

DESCENDING – HENCE IT IS FREE OF CLOUDS.

Schematic of a Hurricane

TROPICAL CYCLONES

• MOIST SURFACE AIR IS TURNED UPWARD AND ASCENDS.

• AS MOIST AIR MOVES UP IT COOLS AND WATER VAPOR CONDENSES.

• THIS PROVIDES LATENT HEAT TO INCREASE BUOYANCY OF THE RISING AIR.

• NEAR THE TOP OF THE HURRICANE THE AIRFLOW IS OUTWARD.

• THE CENTRAL DOUGHNUT AREA OF INTENSE CONVECTIVE ACTIVITY IS CALLED THE EYE OF THE STORM

• EYE WALL CONTAINS STRONGEST WINDS.

Fig. 8-24, p. 229

Fig. 8.29

TROPICAL CYCLONES

• TROPICAL CYCLONES DIMINISH WHEN

• THEY MOVE OVER COLDER OCEAN WATERS

• MOVE ONTO LAND

• REACH A LOCATION WHEN LARGE-SCALE FLOW ALOFT IS UNFAVORABLE

Fig. 8.27

STORM SURGE

Fig. 8.35

TROPICAL CYCLONE DAMAGE

• WIND DAMAGE

• STORM SURGE

• INLAND FLOODING

Fig. 8-39, p. 247