Weather Around The World, 8/1/17: Tropical Cyclones, Heat Waves, And An Eclipse Of The Sun


Home / Weather Around The World, 8/1/17: Tropical Cyclones, Heat Waves, And An Eclipse Of The Sun

Northern hemisphere tropical cyclone season is approaching its yearly maximum in August and September, and both the Atlantic and Pacific Oceans are warm and active. Heat dominates the American west. A drizzle riddle is solved. And solar eclipse fever is rising faster than the temperature in Miami. Let’s go Around The World.

Atlantic, Eastern Pacific, and Western Pacific All Boiling With Tropical Systems

On July 29, the western Pacific hosted two typhoons, a tropical storm, and an area of interest. Satellite photo courtesy of US Navy.

The western Pacific normally has more typhoons annually (16) than the eastern Pacific and Atlantic together have hurricanes (nine and six, respectively). (Note: the definitions of hurricane and typhoon are identical. It just depends on where they are located.).

So far this year, the eastern Pacific has been more active than the other places. But now the western Pacific is a boiling cauldron of tropical trouble.

Taiwan suffered a double whammy last week, as Typhoon Nesat, which had briefly reached category five strength over open ocean, struck the northern coast of the island. Then on Sunday, Tropical Storm Haitang made landfall on the southern coast.

The two storms, much weakened after crossing land and the South China Sea, came ashore in nearly the same place in China’s Fujian Province.

Typhoon Noru is approaching Japan after making a sudden right turn. Graphic courtesy of US Navy.

As of this morning, Typhoon Noru is bearing down on Japan, and is forecast to still be a typhoon when it reaches the southernmost island on Sunday, August 6, 2017.

The Fujiwhara Effect

Two of the eastern Pacific storms, Hilary and Irwin, illustrate a curious effect of interacting tropical systems. Named after  a Japanese meteorologist, the Fujiwhara effect is a dance two tropical systems step to when they get within 500 miles of each other.

The storms rotate counterclockwise around each other. In this case, Irwin pirouetted north towards California while Hilary, after heading northwest, danced off to the southwest.

On July 27, Hurricane Hilary and Tropical Storm Irwin were close enough to do the Fujiwhara tango. Graphic courtesy of NHC.

Some early forecasts suggested Hilary could be nudged far enough north to impact California, but after escaping the influence of Irwin, Hilary waltzed harmlessly out to sea and dissipated over colder water.

Meanwhile, when Irwin escaped the clutches of Hilary, he turned abruptly north and petered out.

Dog Days Of Summer Sizzle In The American West

One of the preliminary indications of changes to the general circulation that is expected with global warming is an increase in the persistence of weather systems. This summer, high pressure has bogged down over the western United States. Underneath this high, skies are generally clear as the air slowly subsides. Subsiding air warms at a rate of 5 F (3 C) per thousand feet, and the clear skies allow the full sun of midsummer to heat the air near the surface to near-record levels. The heat wave, which began in the desert southwest, has spread north and east with the expanding high pressure. Portland, Oregon and Seattle, Washington could set all-time high temperature records in the next few days.

Meanwhile, the desert  has gotten some relief from the seasonal monsoon, as moisture from the Gulf of California and Gulf of Mexico brings clouds and some rain.

Miami, FL Sets Hot Temperature Records

The Miami NBA team picked the right name: HEAT. For sure it was the right name in July, which established several new records, including hottest July overall. In addition, for the first time in history the temperature reached 90° F on every day in July. The string of consecutive 90 degree days has now reached 42, which is the second longest string ever recorded. If the temperature tops 90 for the next three days, it will break the record.

Low temperatures, which are trending higher faster than maximum temperatures, are easily eclipsing all records. For the period January 1 to July 31, 2017, Miami clocked 34 days with minimum temperature 80° F or higher. The old record was 25 days, established in 2010.

The Narrowing Temperature Range

Low temperatures are rising faster than high temperatures for a couple of reasons. First, warm air holds more water vapor than cold. Second, increasing water vapor implies more clouds, which dim the sun’s incoming radiation but trap the earth’s outgoing radiation.

Big cities also play a role in increasing minimum temperatures: Buildings and asphalt don’t radiate as well as natural vegetation.

The Rain In Spain And Ocean Drizzle

Low-level moisture creates fog over the ocean. With gentle updrafts, the fog can become drizzle. Photo courtesy of NASA.

Meteorologists have long recognized that drizzle prefers an ocean environment and suspected that vertical air currents were to blame. Now, NASA has confirmed that this is the case in a study released July 25, 2017.

Except in thunderstorms or major tropical and extra-tropical storms, the vertical motions in the atmosphere are about one-tenth of the horizontal motions. As air rises, it cools and eventually becomes saturated; water vapor begins to condense into liquid water droplets. The strength of the vertical motion determines what type of precipitation falls.

When the air is saturated with moisture as it often is over the ocean, water vapor molecules condense into cloud (at the ground we call a cloud fog) droplets with a typical diameter of .02 mm.

Eventually, cloud droplets merge to form larger drops. An average drizzle drop is .5 mm in diameter, heavy enough to fall through the very gentle updrafts over the ocean.

The slightly stronger updrafts over land are sufficient to keep drizzle drops aloft until they coalesce into larger drops. An average raindrop is 2 mm in diameter, Drops of this size can fall through the normal updrafts over land. As vertical velocities increase, larger raindrops can form. The extreme updrafts in a thunderstorm can keep drops aloft long enough to allow substantial amounts of ice to form on them until they fall as hailstones, which can reach several inches in diameter.

A Midsummer Day’s Night (Eclipse Of The Sun)

Astronomers, casual scientists, and even laymen are agog over the possibility of witnessing a rare celestial event — a total eclipse of the sun. The path of totality will cross the US from Oregon to South Carolina on August 21. Don’t be late; totality lasts for only a couple of minutes at most. The event gives astronomers a chance to see stars that would normally be hidden by the glare of the sun and to observe the effects of general relativity by measuring the bending of light by the gravity of the sun.

This month’s Climate Change Checkup will be published on August 20 and will include the forecast for locations in the path of totality, along with the latest news on global warming. An eclipse forecast update will be published early on August 21, 2017.

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