Weather Around The World, 7/4/17


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Get Ready For The Eclipse

The path of totality of August’s eclipse will enter the US in Oregon and exit in South Carolina. Image courtesy of NASA.

On August 21, 2017 there will be a total eclipse of the sun that can be seen from coast to coast in the US. This is not something that happens every day — more like once or twice a century (the last time was in 1918). And coast to coast has a limited meaning here: the zone of totality stretches from South Carolina to Oregon, but the path of totality is very narrow — less than 75 miles wide. The spectacular effect of the eclipse is really appreciated only within the band of totality.

Then there’s the weather.

The best place to view this eclipse is probably in Wyoming or Idaho, especially the higher elevations, where the probability of clear skies is about 90%. In the eastern states, the probability of good viewing is around 50%.

The likelihood of an unobstructed view of this amazing phenomenon is affected by the time of day. The eclipse starts at 10:15 in Oregon, and will reach Wyoming before noon. Totality will occur around 1 p.m. in Missouri and it will be 2:45 when the sun exits the Carolina coast (All times are local).  Not only are the eastern states normally more humid due to flows from the Gulf of Mexico and Atlantic Ocean (more moisture leads to more clouds), but the afternoon August sun also sets off instability which produces clouds.

A final note: DO NOT look directly at the sun without specialized lenses made for the purpose.  Decoded will publish updates on the weather as the eclipse date approaches.

A Remarkable Coincidence

This image captures a person silhouetted by an annular solar eclipse. Image Credit & Copyright: Colleen Pinski

Viewed from the earth, the sun and moon appear to be the same size: the sun is much bigger and the moon is much closer. Because of the eccentricity of the moon’s orbit (it isn’t round), the moon sometimes appears bigger and sometimes smaller than the sun. When the moon is bigger, there is a total eclipse; when the sun is bigger, it’s called an annular eclipse, during which a slim ring of sun is visible all around the moon.

August’s eclipse is total, but totality will last for no more than 2 minutes and 45 seconds.

NOAA’s July Forecast

July is expected to be hot in the US — big surprise, right? July is the hottest month of the year over much of the northern hemisphere. But according to NOAA’s forecast, issued June 30th, July will be hotter than normal. Average temperatures are forecast from the Great Lakes to the deep south, with warmer than average temperatures prevailing elsewhere. The best chance for above normal temperatures is in Montana.

European Heat Wave

Western Europe as far north as the UK sweltered for much of June, and the  heat moved east into Greece, Turkey, and the Balkans towards the end of the month. On the last  day of June, Antalya, Turkey’s temperature soared to 45° C (113° F). A low pressure area has brought some relief in the last couple of days, but the forecast calls for high pressure to build again and abnormally hot weather to return over much of southern Europe during July.

Northern Hemisphere Heads Towards Peak For Tropical Activity

The Atlantic hurricane season is only a month old but has already been unusually active with four named storms to date. Seasonal peak does not occur until early September, but if conditions across the Atlantic Ocean persist through the summer, this could be an active and destructive season. Decoded Science does not make this statement to be alarmist, just practical. Even in the most active seasons, most people don’t see the effects of a hurricane. While those who do ……. (sound of waves breaking and wind howling).

In most years, easterly waves coming off Africa fall apart in June and most of July because the water is cool and there is vertical shear (change of wind with height) which tears the systems apart.

This year, the water is warmer than normal and the shear is low, and several waves have held together all the way across the ocean. Most of the powerful Atlantic hurricanes have originated in the area of the Cape Verde Islands off the African coast, and if the current conditions persist into August, the chance of a blockbuster hurricane will be much greater than in a normal year.

Meanwhile, the western Pacific has been unusually quiet for many weeks. A weak tropical storm is currently crossing Japan.

Indian Monsoon: So Far, So Good

The Indian monsoon has overspread all but the far north of the country. There was also a tropical storm approaching Japan as of July 3. Image courtesy of US Navy.

Last year’s monsoon in India delivered rainfall that was well below average, adversely affecting agriculture, which accounts for one-fifth of the country’s economy.

El Niño was blamed, as this Pacific Ocean temperature anomaly is inversely correlated with monsoon rain. This year, conditions in the Pacific are neutral (neither El Niño nor La Niña) and the June rain in India was close to normal. Forecasts now call for the Pacific to remain tame and monsoon rainfall to be near normal for the season.

The monsoon rains were distributed fairly evenly around the country, which is another positive. Average over the country doesn’t do much good if there are wild swings from one place or time to another. Recently some parts of the northeast have received nearly a foot of rain in 24 hours, receiving a nationwide monthly average of rain in a single day.

Arizona Has A Monsoon, Too. Don’t Laugh.

The Indian Monsoon can be compared to a giant wave breaking on the beach as the monsoon front pushes ashore and eventually overspreads the entire Indian subcontinent. Phoenix, Arizona has a monsoon, too, but it’s like melting snow coming down a mountain and reaching the valley as a tiny trickle. Still, a monsoon is a monsoon, and the arrival of moisture from the Gulf of California and the Gulf of Mexico has an effect on the desert. The average monthly rainfall in Phoenix is .04 inches in June and over an inch in July. Plants bloom, most importantly grasses on which livestock feed, and the sweltering heat is kept to the low 100s.

Coming Up

For several weeks, the carbon dioxide measurements on Mount Mauna Loa, Hawaii have been falling. Is Paris working? Will global warming subside? Find out in Decoded Science’s mid-July Climate Change Checkup.

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