The latest weekly ENSO report from the Climate Prediction Center (CPC) has three consecutive weeks of La Niña threshold temperatures in region 3.4 of the Pacific Ocean. The La Niña threshold is a temperature anomaly of -.5 degrees Celsius or cooler for three consecutive months. We are in the third consecutive week of -.5 or cooler. If an average anomaly of -.5 or cooler continues for nine more weeks, we are officially in a La Niña. So, the earliest that CPC would declare La Niña is early to mid October. That is towards the end of Atlantic Hurricane Season, not very helpful.
Weekly tracking is significant now because of the historical relationship between La Niña conditions in August, September and October (ASO) and the Atlantic Hurricane Season. La Niña conditions during ASO, the heart of the Atlantic Hurricane Season, matched with historical data show a significant statistical increase over the long-term average in named storms, hurricanes, major hurricanes and landfalls, hurricane landfalls and major hurricane landfalls in the United States.
Not only is there an increase in the number of storms and land falling storms, but there is an increase in ACE. ACE is a measurement of energy in tropical systems. The National Hurricane Center uses ACE ( Accumulated Cyclonic Energy ) to measure the amount of energy during the lifespan of each storm and in each hurricane season. Since 1950, here are the averages by phase during ASO:
On August 2nd, Earl formed in the central Caribbean Sea. This is the fourth named storm of the 2016 season. Earl is forecast to make landfall in Belize as a category 1 hurricane. If you are looking for Earl updates or the latest on the tropics, use this link to the National Hurricane Center. Here is a link to the radar in Belize.
So moving forward, there are many important questions. Will La Nina conditions continue each week? If so, historically, look for above average weather in the tropical Atlantic through fall. Are other factors that impact tropical development ( dry air, water temps, tropical waves, Sahel Rainfall anomalies) negative, neutral or favorable. Is Earl’s track a pattern that repeats based on the strong ridge over the central United States? If so, Florida, the Gulf Coast, Yucatan and Caribbean could see a higher than average threat, but that is still to be determined. Ridges move, especially in September and October.