Tag Archive for: La Niña

NWS Says La Niña Has Ended, Likely Impact on Weather

On March 9, 2023, the Climate Prediction Center of the National Weather Service (NWS) announced that La Niña conditions which persisted for 3-years have finally ended. But we are not shifting directly into El Niño. Instead, we’re entering a transitional phase. NWS expects neutral conditions to continue through the Northern Hemisphere into spring and early summer of 2023.

La Niña and El Niño represent opposite phases of what meteorologists call ENSO, the El Niño Southern Oscillation in the Pacific Ocean. They govern recurring climate patterns across the tropical Pacific and have a cascade of global side effects, says NWS.

The patterns shift back and forth irregularly every two to seven years. This past La Niña phase lasted three years, an unusually long time.

NWS predicts that ENSO-neutral conditions will continue through the spring. The weather service also predicts El Niño conditions to form during summer 2023 and persist through the fall.

Impacts on Weather

The oscillation brings predictable shifts in ocean surface and atmospheric temperatures. These shifts disrupt the wind and rainfall patterns across the tropics.

El Niño brings cooler, wetter conditions to the southern U.S. in winter months. It also brings stronger steering currents that can disrupt low-pressure systems coming off the coast of Africa that turn into hurricanes.

La Niña, on the other hand, usually means less disruption, more Atlantic storms, and deeper droughts in the southern U.S. But we’re finally putting the most recent La Niña behind us.

ENSO Influence on Atlantic and Pacific Hurricane Seasons

The continental United States and Caribbean Islands have a substantially decreased chance of experiencing a hurricane during El Niño and an increased chance of experiencing a hurricane during La Niña. These maps (by NOAA Climate.gov, based on originals by Gerry Bell) explain why.

Typical El Niño effects on Pacific and Atlantic seasonal hurricane activity.

Overall, El Niño contributes to more eastern and central Pacific hurricanes and fewer Atlantic hurricanes. Conversely, La Niña contributes to fewer eastern and central Pacific hurricanes and more Atlantic hurricanes – exactly the opposite.

Typical La Niña effects on Pacific and Atlantic seasonal hurricane activity.

Other Influences on Hurricane Formation: AMO

NOAA also says that other oscillations, such as the Atlantic Multi-Decadal Oscillation (AMO) also influence hurricane formation. The warm phase of the AMO is associated with warmer sea surface temperatures and high hurricane activity in the main development region of the Atlantic between Western Africa and the Caribbean.

“The hurricane activity in any given season often reflects a combination of the multi-decadal signals and ENSO,” says NOAA.

For More Information

For a fuller discussion of how El Niño and La Niña influence other aspects of weather worldwide, check out NOAA’s Climate.gov, especially the FAQ page.

Also, the Associated Press ran an interesting story this morning by Seth Borenstein. The headline: “La Nina, which worsens hurricanes and drought, is gone.”

Borenstein says NOAA gives El Niño a 60% chance of returning this fall. But there’s also a 5% chance that La Niña will return for an unprecedented fourth winter.

We should have more certainty in a few months.

Posted by Bob Rehak on 3/9/23

2018 Days since Hurricane Harvey

Iota Could Drop Another 20-30″ of Rain on Areas Just Devastated by Eta

Nicaragua and Honduras, devastated by Hurricane Eta just a little more than a week ago by up to 40 inches of rain, could see another 20 to 30 inches from Iota. Iota formed today in the central Caribbean.

Meanwhile, people in Central America are still digging out from landslides, trying to restore their homes from floods, and dealing with loss of crops, airports, roads and other infrastructure.

Two Major Hurricanes in Two Weeks

Eta hit Nicaragua a little more than a week ago as a Category 4 storm, killing at least 120 people in flash floods and landslides in Central America, according to the Associated Press.

Forecasters say that Iota could also rapidly intensify into a major hurricane, given ideal conditions in the Caribbean.

To put these monster rainfall totals into perspective, Harvey dumped an average of approximately 45 inches across 1000 square miles in the Houston Area. Three years later, we’re still trying to recover.

The combination of these two storms could mean 50% more rain in Central America than Houston received during Harvey.

Forecast track for Iota

NHC Forecast

The National Hurricane Center says that Iota’s maximum sustained winds have increased to near 40 mph with higher gusts. Steady to rapid strengthening is likely over the weekend, and the system is forecast to be a major hurricane when it approaches Central America.

Across remaining sections of Central America, the system has the potential to produce 20 to 30 inches of rain with a focus across northern Nicaragua and Honduras. This rainfall would lead to significant, life-threatening flash flooding and river flooding, along with landslides in areas of higher terrain.

The environment ahead of Iota appears to be quite conducive for intensification. The system will be moving over warm waters, in a moist atmosphere, and within an area of very low vertical wind shear. As a result, steady to rapid strengthening appears likely over the next few days.

Record-Setting Season

“Iota is the record 30th named storm of this year’s extraordinarily busy Atlantic hurricane season,” said the Associated Press.

Eta may also have tied or exceeded Gordon for the longest-lived tropical event. Gordon formed on November 8, 1994 and dissipated almost two weeks later on November 21. Hurricane Eta formed on October 31 this year and dissipated today, November 13. Thus, it may have lasted a day longer. However, the experts have not yet made an official announcement that I have seen.

Why Such a Busy Season?

Dr. Nelun Fernando, a climatologist writing for the Texas Water Development Board, says, that currently we are under the influence of La Niña. “You can think of El Niño and La Niña as two faces of the same coin, where the coin is a phenomenon known as the El Niño Southern Oscillation (also referred to as ENSO).”I

“La Niña is associated with a more active Atlantic hurricane season,” he says. “This increased activity is because the vertical wind shear (the change in wind speed and direction with height) is weaker during a La Niña year, enabling tropical storms to develop vertically without impediment.”

In La Niña years, steering currents that could cause wind sheer shift farther north, letting more storms develop in the tropical Atlantic.

Posted by Bob Rehak on 11/13/2020

1172 Days After Hurricane Harvey