1
00:00:00,000 --> 00:00:05,000
We saw in the weather update that the storm in the Atlantic Ocean is now tropical depression.

2
00:00:05,000 --> 00:00:08,000
We're afraid that it's going to affect our trip to Tampa.

3
00:00:08,000 --> 00:00:12,000
So we need to know, how does a storm grow and become a hurricane?

4
00:00:12,000 --> 00:00:16,000
First, you need to know a little bit about pressure systems and how they form on Earth.

5
00:00:16,000 --> 00:00:20,000
We learned about air pressure from Dr. D. Is this the same thing?

6
00:00:20,000 --> 00:00:23,000
There are two types of air pressure systems, high and low.

7
00:00:23,000 --> 00:00:27,000
The uneven distribution of the Earth's surface causes them to form.

8
00:00:27,000 --> 00:00:31,000
So you mean that's why it's hotter at the equator than at the north and south poles?

9
00:00:31,000 --> 00:00:36,000
Exactly. And we also have local temperature variations depending on the land's surface type.

10
00:00:36,000 --> 00:00:41,000
These local temperature variations cause air to rise in some areas and to sink in other areas.

11
00:00:41,000 --> 00:00:45,000
This rising and sinking motion causes high and low pressure areas in the atmosphere.

12
00:00:45,000 --> 00:00:49,000
What do high and low pressure systems have to do with the tropical storm?

13
00:00:49,000 --> 00:00:53,000
We have regions in the tropics that are warmer and cooler than other regions.

14
00:00:54,000 --> 00:00:58,000
Low pressure forms in the warm regions and once they form, they move from east to west.

15
00:00:58,000 --> 00:01:03,000
I remember we learned in the case of the mysterious red light that winds in the tropics are called trade winds.

16
00:01:03,000 --> 00:01:08,000
These winds move from the east to the west. Is that why they move in a westerly direction?

17
00:01:08,000 --> 00:01:12,000
Yes, and as low pressure areas move over the warm tropical oceans,

18
00:01:12,000 --> 00:01:16,000
they gather heat and moisture from the ocean and cause thunderstorms.

19
00:01:16,000 --> 00:01:20,000
The rain and the thunderstorms warms the atmospheric air column.

20
00:01:20,000 --> 00:01:24,000
That causes the surface pressure to lower, thus strengthening the low pressure area.

21
00:01:24,000 --> 00:01:28,000
So as the warm air rises, the pressure in the system gets cooler.

22
00:01:28,000 --> 00:01:33,000
Something like that. The middle and upper atmospheric winds take away air from the low pressure areas

23
00:01:33,000 --> 00:01:36,000
and deposit them in the high pressure areas.

24
00:01:36,000 --> 00:01:42,000
And we end up with very small but intense low pressure areas and very weak but large high pressure areas.

25
00:01:42,000 --> 00:01:44,000
And what's the third way?

26
00:01:44,000 --> 00:01:46,000
That happens when a hurricane forms an eye.

27
00:01:46,000 --> 00:01:50,000
An eye? I know he doesn't mean a real eye.

28
00:01:50,000 --> 00:01:55,000
No. No, it's the center of the hurricane where there is no cloud.

29
00:01:55,000 --> 00:02:00,000
Air is sinking near the center of the hurricane and as it sinks, it warms up dramatically.

30
00:02:00,000 --> 00:02:04,000
That warming causes the hurricane to intensify rather dramatically.

31
00:02:04,000 --> 00:02:09,000
Dr. V told us that wind is formed when air moves from an area of high pressure to an area of low pressure.

32
00:02:09,000 --> 00:02:12,000
Do the winds of a hurricane increase as the pressure drops?

33
00:02:12,000 --> 00:02:17,000
Yes, and the winds typically increase as you move toward the eye or the center of the hurricane.

34
00:02:17,000 --> 00:02:20,000
In strong hurricanes, the winds can vary rather dramatically.

35
00:02:20,000 --> 00:02:23,000
About 20 miles per hour on the outskirts of the hurricane

36
00:02:23,000 --> 00:02:28,000
to more than 150 miles per hour near the center in the eye wall of a hurricane.

37
00:02:28,000 --> 00:02:31,000
Is the wind the fastest in the eye?

38
00:02:31,000 --> 00:02:34,000
Actually, that's a common misconception. It isn't.

39
00:02:34,000 --> 00:02:39,000
The winds are strongest just outside the eye and decrease rather dramatically toward the circulation center

40
00:02:39,000 --> 00:02:41,000
where they're oftentimes light and variable.

41
00:02:41,000 --> 00:02:43,000
Sounds like a place to be in a hurricane.

42
00:02:43,000 --> 00:02:47,000
Is there a particular time of year hurricanes are more likely to form?

43
00:02:47,000 --> 00:02:49,000
That's a great question.

44
00:02:49,000 --> 00:02:52,000
And in the northern hemisphere, it's June through November

45
00:02:52,000 --> 00:02:56,000
when the sea surface temperatures are warmest and the land areas are hottest.

46
00:02:56,000 --> 00:02:58,000
It's ideal for hurricane formation.

47
00:02:58,000 --> 00:03:00,000
You've given us a lot to think about.

48
00:03:00,000 --> 00:03:02,000
You're welcome. I'm glad I could help.

49
00:03:02,000 --> 00:03:07,000
Be sure to watch the Weather Channel for all the tropical storm and hurricane advisories and updates.

50
00:03:07,000 --> 00:03:12,000
You also might want to visit the NASA Y-Files website's research rack

51
00:03:12,000 --> 00:03:14,000
and check out the link to the Weather Channel.

52
00:03:14,000 --> 00:03:16,000
We will. Thanks. Goodbye.