La Niña Conditions Subsiding To ENSO Neutral Could Bring More Storms

Hurricane Season in the Northern Hemisphere is approaching. The Atlantic Hurricane Season is now less than a month away, and the Eastern Pacific Season is going to be starting up in five days. While both seasons end on November 30th, the Eastern Pacific gets a two week jump on the Atlantic. The earlier start in the Eastern Pacific is based upon data collected on these storms since 1949. About 90 percent of storms in both the EPAC and Atlantic occur between the start and end dates for their seasons.

On average, the Eastern Pacific gets about 16 named storms per season. Of those 16 named storms, about 9 of them become hurricanes, and four of those intensify to major hurricane status. The Eastern Pacific Basin is the second most active basin in the world next to the Western Pacific. Originally, before the era of satellites, the Atlantic was thought of as the second most active basin, but forecasters were proven wrong once they were able to get another set of eyes in space.

Extremes for this region have been a maximum of 28 named storms, 16 hurricanes, and 10 major hurricanes while there has been a minimum of 8 named storms, 3 hurricanes, and no major hurricanes. A very important variable in the Eastern Pacific Hurricane Season forecast is the presence of either El Niño or La Niña. These phenomena have become very important ingredients in our global climate. El Niño occurs when sea surface temperatures in the Eastern Pacific are warmer than average. This climate shift usually coincides with Christmas time in South America, and that was why it was first called El Niño by Peruvian fishermen.

La Niña is when the opposite happens. Cooler than normal sea surface temperatures in the Eastern Pacific. When there is an El Niño that usually means a very active hurricane season in the EPAC. During La Niña, the Atlantic is usually busy. Why is that? Hurricanes thrive in warm water where the temperature is 80 degrees fahrenheit or better. Warm water is where these storms get their fuel. So, when an El Nino occurs, the sea surface temperatures are heated up to become very favorable for Eastern Pacific storms. The development of more storms in the EPAC then creates more of a shearing environment at the upper levels in the Atlantic, which inhibits Atlantic storms.

Conversely, the cooler water hinders storm development in the Eastern Pacific. The fewer EPAC storms, the less turbulence and wind shear in the upper levels of the atmosphere in the Altantic. As a result, Atlantic Hurricanes have less barriers to their development. With all of that said, the current state of the climate in the Eastern Pacific is in transition from La Niña to ENSO neutral. So, sea surface temperatures there are expected to be more normal during hurricane season. As a result, we could see a bit more activity than in recent years.

Historically, storms in the Eastern Pacific do not make direct impacts in the United States as hurricanes. There are exceptions though such as the 1858 San Diego Hurricane, and the 1939 Long Beach storm. The reason for this is because once you get north of Baja California in Mexico, the water temperatures are much cooler, and hinder the development of hurricanes. An example of this was in 1997 when Hurricane Linda became a monster Category Five storm in the Eastern Pacific. Back then, there was talk of the storm impacting Southern California, and there was file footage of the 1939 storm on television. However, the storm dissipated well to the South of San Diego.

Impacts from Eastern Pacific storms in the United States is usually in the form of high surf along the California coast, and soaking rains for the Southwestern United States. However, arid conditions over the Desert Southwest can take the moisture out of those remnants. Hurricane Nora was an example of this, and was given the nickname, Hurricane No Rain.