A couple of hurricanes. One west of Mexico. The other to the east over the Gulf of Mexico. One over the Pacific Ocean. The other in the Atlantic Ocean. These are hurricanes Nora and Ida. A typical August image that marks the beginning of the heyday of hurricane season in the tropics.
This Saturday afternoon’s satellite image showed the category 1 hurricane Nora on the coast of Jalisco in Mexico with a minimum central pressure of 977 hPa and a wind of 130 km/h. It is visible further east, over the Gulf of Mexico is Hurricane Ida which very quickly gains intensity.
The US National Hurricane Center forecasts that Nora will head north along the coast of Mexico towards the Baja California region.
On the other hand, Ida moves quickly towards the South of the United States, where he must land in the state of Louisiana.
Ida is the hurricane that worries the most.
Ida, according to the latest projection by the US National Hurricane Center, is expected to reach the south coast of New Orleans as a devastating category 4 hurricane on the Saffir-Simpson scale that goes up to 5, with destructive winds of 250 km/h, torrential rains with extreme volumes and tidal elevation of up to five meters in the coastal strip.
The storm that passed through Isla de la Juventud in Cuba between late Friday and early Saturday is now gathering strength over the very warm waters of the Gulf of Mexico and with an atmosphere of low wind divergence, conditions that favor rapid intensification.
The National Hurricane Center warned of “life-threatening flooding” due to the steep rise of the sea off the coast and “potentially catastrophic wind damage” in areas close to where the hurricane enters land. New Orleans has been placed under a hurricane alert.
peak of the season
This is the time of year for the big hurricanes.
The climatology period between August and October, with the warmest waters, marks the peak of the tropical hurricane and cyclone season, which are quite frequent in the East Pacific and North Atlantic. Ida is expected to land in Louisiana on the same day in 2005 that devastating Hurricane Katrina hit the New Orleans area.
Several factors contribute to the seasonal increase in tropical cyclones starting in August:
First, the Eastern waves emerging from Africa are more organized and stronger, usually serving as the starting point for the formation of tropical storms and hurricanes in the North Atlantic. Of most concern are those that arise near Cape Verde in the so-called Main Development Region (MDR), an area where waves (areas of lower atmospheric pressure) tend to give rise to some of the most intense hurricanes that later reach Central America and the United States.
Yet, the dust plumes advancing from the Sahara, which carry dry air and normally reduce the occurrence of instability, tend to give way in August, as the increasing frequency of waves from East Africa gradually raises the humidity.
Also, wind shear (divergence), the change in wind speed and/or direction at altitude, which can inhibit the formation of a potential tropical cyclone, tends to be low at this time.
Finally, sea surface temperatures rise toward their peak in early autumn in the Northern Hemisphere (September). With warmer ocean and greater latent heat, the atmosphere’s ability to generate convection (storms) to help trigger tropical cyclones also increases towards the peak of autumn.
The Main Development Region
Much of the increase in tropical cyclones at this time of year, between August and October, takes place in a key area of the Atlantic Ocean that is becoming more conducive to tropical systems.
The area called the Major Development Region, or MDR for its acronym in English, lies in the open sea in the Atlantic Ocean between the Caribbean and the west coast of Africa. This region is called the main development region because it is responsible for 60% of all named storms that form in the Atlantic and 85% of all hurricanes that form.
The region allows weak tropical waves off the coast of Africa to transform into tropical storms and hurricanes as they move west over much warmer waters and a vertical wind profile with much less divergence that favors the rapid intensification of tropical systems.