The weather cannot seem to behave in moderation these days.
Last week, the tropics were full of dangerously whirling cyclones; this week, all’s calm on the equatorial front.
Parts of Texas, bone-dry for a month, are now setting records for rain.
The jet stream has turned active as the northern hemisphere heads towards winter.
And an asteroid will come closer to Earth on Halloween than will any similar-sized object for more than a decade.
Oh, yeah, the World Series starts tonight — it’ll be cold, and maybe rainy.
Let’s go Around The World.
Wild Swings In Texas Weather
The state that is known for doing everything BIG is living up to its reputation when it comes to precipitation records. Last week, record rains fell after 34 days without a single drop in some cities. The changes are a result of schizophrenic flows from, alternately, the Gulf of Mexico and the deserts of the southwest.
‘Strongest’ Hurricane Patricia Threads The Needle; Mexico Avoids Catastrophic Damage
Hurricane Patricia exploded into a category five storm from a category one storm in just a day. After landfall, it went from category five to barely discernible as a remnant circulation in a day. In between, the storm was classified as the most powerful hurricane ever in the Atlantic or eastern Pacific — but with a lot of caveats.
First, the effects:
Nobody died in this storm and though several thousand houses were destroyed, the cost will be relatively low. The hurricane came ashore in a sparsely populated area, about midway between Manzanillo and Puerto Vallarta, two modest-sized cities, and petered out in the mountains before reaching the major metropolis of Guadaljara. Because the storm was relatively small in diameter, the most powerful part of the storm did not reach any heavily populated areas.
Calling this storm the strongest is a little bit of a stretch. For one thing, no one was on the ground when the winds in Patricia allegedly reached the magical speed of 200 miles per hour. If there were, the accuracy of the reading would be in doubt: Anemometers are not built to be accurate in that kind of wind.
The wind measurement was made from an airplane. This is tricky business, measuring wind speed from an airplane moving a hundred miles per hour itself. And the measurement is not taken at the surface.
Accurate measurements of maximum wind in a hurricane have never been made, so to classify this one as the biggest is somewhat misleading. Don’t get me wrong: It was a powerful storm. But it is likely that others were stronger.
Eyewitness accounts from colonial times indicate very strong storms in the Atlantic, particularly The Great Colonial Hurricane of 1635.
Why Does A Tropical Cyclone Undergo Explosive Development?
Wind depends on pressure gradient (difference of pressure over distance).
A powerful cyclone has a very low central pressure. The circulation is simple (the following motions are for the northern hemisphere; in the southern hemisphere, everything is reversed):
- Air circulates counterclockwise in the lower part of the storm and spirals slightly inward.
- Air spirals upward counterclockwise in the lower portion, but since the center of the storm is very warm, the central column expands (warm air has greater volume than cold).
- In the top half of the storm, the pressure gradient is reversed and the wind spirals clockwise and slightly outward.
- The difference between the amount of air flowing out at the top and in at the bottom causes the pressure to drop. In a developing or mature hurricane, the outflow at the top is clearly shown by the high clouds on a satellite photograph.
The record-setting year for tropical cyclones in the Pacific clearly is related to the much-warmer-than-normal water associated with El Niño. Tropical cyclones feed off the energy of warm water.
But Patricia also found a sweet spot of vertical wind shear (change of wind with height), which can tear apart a tropical system: There was none. When a hurricane can develop in an environment of little wind shear and high ocean temperature, very rapid development can take place.
The final factor for Patricia was the lack of inhibiting feedback from upwelling of colder water; the water off Mexico is warm to considerable depth.
All Things Are Relative: Close Encounter Of An Extraterrestrial Kind
Newly-discovered asteroid 1915 TB145 will pass within 300,000 miles of Earth on Saturday.
This seems pretty far away — farther than the moon — but it is a fraction of an inch in terms of distances in the universe — even those in our solar system.
Since the asteroid was not discovered until two weeks ago, and since a similar object colliding with the earth almost certainly caused a major extinction event 65,000,000 years ago (bye-bye dinosaurs), this object, which for so long avoided detection, has to make one wonder: It happened before; it will surely happen again; could it happen soon?
If you have a telescope and want to get up about three o’clock Saturday morning, look in the direction of the constellation Orion and you might catch a glimpse of this wandering hunk of rock.
No Eclipse, But Maybe Bigger Tides
Last month’s full moon and eclipse coincided with lunar perigee (closest approach to the earth), and the result was extremely high tides. This month there won’t be an eclipse, as the point of perigee has moved (it’s a complicated physical process called precession), but perigee will be only a day after full moon. The tides may be higher than those last month in places where the wind blows the water onshore — the northern Gulf and south-Atlantic coasts.
World Series Begins Tonight
The World Series between the Kansas City Royals and the New York Mets begins in Kansas City tonight. The weather will be cool — temperatures in the 50s — and there could be some rain from the moisture connected with the remnants of Hurricane Patricia. The circulation is now extra-tropical and centered in Louisiana.
The Jet Stream Is Active
On cue as the season changes, the jet stream has become more vigorous. A large storm in central Canada could be the signal that El Niño will bring more rain than snow to the United States as moisture and warmth push northward into the jet stream systems. Let Decoded Science know what the onset of winter looks like where you live.