Mother Nature is upstaged by the President of the United States as Atlantic hurricane season begins. The Indian monsoon sweeps ashore as a related tropical cyclone kills six in Bangladesh. The remnants of a Pacific Tropical Storm usher in Florida’s rainy season. And there’s more. Let’s go Around The World.
Atlantic Hurricane Season Starts With A Whimper
The Atlantic Basin Hurricane season officially began on June 1, 2017, despite the fact that a storm formed out-of-season in May for the third year in the last four.
Currently there is no activity in the Atlantic Ocean, Gulf of Mexico, or Caribbean Sea. The month is likely to continue that way; a hurricane forms only once every five Junes. And those that do form are generally minimal. There have only been two major (category three or higher) June hurricanes in the Atlantic Basin since 1950 — none in the last 50 years.
The Central and Eastern Pacific Oceans are also quiet. The former season started June 1, 2017, while the latter began May 15, 2017.
Weak Tropical Storm Beatriz impacted Mexico last week, but Eastern Pacific water temperatures are generally cooler this year than last, particularly in the path between the tropical storm breeding ground south of Mexico and the Hawaiian Islands. Storms normally die over the cold water, but last year it was warm enough to allow several storms to threaten the islands.
Indian Monsoon Is On Schedule
The Indian Monsoon arrived on the mainland about two days early — on May 30, 2017. The Monsoon will move north, reaching Delhi by the end of June. Indian agriculture depends on monsoon rain, and last year’s monsoon was late arriving and weak in total rainfall. Since agriculture accounts for about 20% of the Indian economy, the monsoon’s regular occurrence is important to the economy as well as in ending the intense heat that precedes it.
Last year’s monsoon was affected by the La Niña in the Pacific Ocean; there is a significant negative correlation between the strengths of La Niña and the monsoon. With neutral to slightly El Niño conditions this year, more normal rainfall is expected, and the slightly early onset of daily deluges at the coast is a good sign.
As frequently occurs, a tropical cyclone formed on the monsoon front and made landfall in Bangladesh on May 29, 2017 with nearly hurricane force winds. Tropical Cyclone Mora killed six people and destroyed thousands of homes.
What Is A Monsoon And What Causes It?
All beachcombers are familiar with daily land and sea breezes. During the day, the sun heats the land more than the ocean because water distributes the sun’s radiation while land holds it at the surface. The heated land warms the lower atmosphere by conduction and the warm air rises. This begins a local circulation in which the air sinks over the ocean and moves from ocean to land at the surface (and from land to sea aloft). At night a reverse circulation forms, creating a land breeze.
A monsoon can be viewed as a seasonal sea breeze that affects large land areas including some far from the ocean. The land heats during summer and cools during winter. The summer flow from ocean to land can contain large amounts of water vapor, and if other atmospheric conditions are in place, such as continental lift, the accompanying rains can be heavy. All the factors needed to make a powerful monsoon exist in India.
Florida Rainy Season Begins; Fire Danger Reduced
Florida has a unique sea breeze. Since it is a peninsula, Florida gets a sea breeze on both east and west coasts. When they meet in the spine of the state, the lifting is particularly powerful. Florida also sits in the zone near 30 degrees latitude which separates the tropical easterlies from the mid-latitude westerlies. Pressure is normally high and the air has a slight subsidence.
The atmospheric circulation over Florida is in a perpetual tug-of-war between the general tendency of the air to subside and the sea breeze effect which makes air rise. During the winter, cold fronts bring dry air from the north and the lack of moisture leads to a dry season from November to May. From June through October, enough moisture is present to allow for a rainy season.
The average date for the rainy season to begin is May 23, but this year it was delayed until June 2. Then a pulse of moisture associated with the remnants of Tropical Storm Beatriz crossed Mexico and the Gulf of Mexico and brought an abrupt end to the dry season.
The onset of the rain also diminished the fire danger, which had become extreme in the center of the peninsula due to a drier than normal winter and the delay in the start of the rain.
US Withdraws From Climate Accord
Until last week, there were 195 signatories to the Paris Climate Agreement. Now there are 194. US President Donald Trump announced that The United States will join Nicaragua and Syria as the only countries that belong to the United Nations Framework Convention on Climate Change who are not signed on to the agreement.
In terms of greenhouse emissions policy, there isn’t much difference between being in or out of the agreement. All the emissions reductions are voluntary. But the agreement has symbolic meaning in that the signatories recognize there is a problem and agree on at least the beginnings of a way to fix it. Whether the withdrawal from the agreement by the world’s largest major per capita emitter (a couple of very small countries have higher per capita emissions than the US) will have worldwide influence is not yet known.
Decoded Science will have more to say on this subject in the mid-month Climate Change Checkup.