(1/2) Formidable Tropical Cyclones. Why Hurricanes never hit California

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Aug 29, 2017 03:20
Recently, there’s been lots of coverage of the hurricane Harvey hitting Texas. Many places have been flooded and many people have lost their homes. Seeing this hurricane’s wrath on TV made me feel like the Hurricane Katrina just happened not long ago.

Hurricane and Typhoon are technically the same thing. We name cyclones in the Atlantic “hurricanes” and those in the near-Asia Pacific “typhoons.” The US has East and West Coast, but I rarely or never heard a cyclone once hit the American West Coast. Why do tropical cyclones tend to strike Florida, Louisiana, and Texas, but not California?

I did a bit searching and got an answer. There are two reasons. The first is that, thanks to the Earth’s rotation, the storms that form in the tropics tend to blow from east to west. The answer didn’t explain why, but I speculated that it’s because the air above land moves slower than the Earth’s crust. The planet spins eastwards. The air lags behind so it appears to move from east to west. The answer also said that the tropical winds blow from south to north (in the Northern Hemisphere) and didn’t explain about it either. My understanding is that the airflow/fluid tend to move along the tapering direction of an object. For the northern hemispheric part of the Earth, it’s from south to north.

The other reason is that tropical storms feed on warm sea water. The waters near California are not warm enough to foster a tropical cyclone. Reading this line, I went to check the map of the US and saw California is indeed on a higher latitude than Florida. It was also interesting to find that the Caribbean Sea is almost on the same latitude of the South China Sea, where typhoons constantly form!

Things all became clear to me. Tropical storms that formed in the Caribbean Sea or the Gulf of Mexico may travel northwest to Texas, or blow straight north to Florida or even New York City! However, the tropical storms that formed to the west of Mexico may head for Hawaii, but will never detour to California. I have also come to realize why California climate is so dry most of the year, while the US southeast is much damper. It’s partly because humidity brought by tropical winds visit Florida but not California!
最近有很多关于飓风哈维袭击德州的报道。很多城市被洪水淹没,不少人流离失所。在电视上看到这次飓风灾难的情景,感觉卡特里娜就发生在昨天一样。

其实,飓风和台风是一回事。我们把大西洋的热带风暴叫做飓风,亚洲一带的太平洋风暴叫做台风。美国有东西海岸,我几乎没有听说过热带风暴袭击过美国西海岸。为什么热带风暴常常袭击佛罗里达、路易斯安那和德克萨斯,却不光顾加州呢?

我在网上查了下资料,找到了答案。主要有两个原因,第一个原因是,由于地球的自转,热带地区形成的风暴常常由东向西运动,答案没有解释为什么,我猜想可能是因为空气比地表运动速度慢。地球向东转,空气速度要慢些,所以感觉是从东往西运动。答案还说,在北半球,热带洋风常常从南向北运动,但也没有给原因。我的理解是,空气和液体往往沿着物体的下沿走,在地球北半球,气体当然沿着赤道往北极方向走。

第二个原因是,热带风暴的形成对水温也有要求,加州附近海域的水温不够形成热带风暴,看到这里,我去查了一下美国地图,发现加州的纬度确实比佛罗里达州要高。我还惊奇地发现,加勒比海和中国南海差不多一样纬度,后者也经常形成台风。

这样的话,事情就都清楚了。加勒比海域,或者是墨西哥湾形成的热带风暴向西北刮去就会到德克萨斯,如果直接向北,就会到佛罗里达州,甚至可以到纽约。但墨西哥以西洋面形成的飓风,可能会去夏威夷,但不会绕路去加州。想到这里,我也明白了为什么加州那么干旱,而美国东南部却那么潮湿了。部分原因是热带海风携带者大量水分,能到佛罗里达,却到不了加州!