La Nina's effects not going quietly into the night
The ENSO (El Nino-Southern Oscillation) is an Oscillation which has been stuck in a La Nina phase for the past 2 years. One could argue that some of the foundations of the prolonged La Nina were already in place during the 2009-10 El Nino. There was the interesting characteristic of a non-El Nino-like excessive rainfall and flooding in northern Australia during that period.
La Nina generates a situation that leads to amplified, blocked weather patterns by the effect on global atmospheric angular momentum (AAM) by the cooling of the waters of the equatorial Pacific. In general this means that ridges of high pressure dominate east of mountain ranges and land masses and troughs to the west, The excessive heat of last summer and our recent non-winter were extreme examples of what La Nina can do.
Finally the pendulum is shifting in the El Nino direction but it appears that late Spring and early Summer will contain some lingering blocked weather patterns and hurricane potential. Therefore, the hottest days of summer appear to be slated for June. This chart shows the hole that AAM must climb out. The trend will be our friend as weather patterns evolve into El Nino solutions but it will take some time for the uptrend toward cooler/milder summer weather can take over.
|The AAM line is back in La Nina territory|
In general there is an uptrend from March lows.
June: The hottest month featuring the warmest days and I completely expect a streak or two of 95+ degree highs.
July: I would not be surprised if the warmth of June ends in an East Coast or NE Gulf Tropical Storm. Cooler than average to moderate.
August: Near average temperatures with some back and forth as late summer processes attempt and ultimately fail to sustain a prolonged Bermuda High.
If not for some above average Atlantic Ocean temperatures in key regions (+AMO) it would be easy to see summer here in Central NC and VA to be below average. The Ocean surface temperature variation is also a known Oscillation that is heading toward a negative dominant phase but not there yet.
Summers heading into an El Nino tend to not include high numbers/intensity of tropical storms. Westerly upper level winds in the tropics inhibit storm development. Overall activity should be below long term averages.
Storm tracks tend to recurve out to sea more quickly than La Nina seasons. They also form north of the deep tropical regions and closer to land. We call this "Homebrew" development. Those storms are often weaker than the Cape Verde type hurricanes but there is far less warning before landfall.
Lingering low AAM is likely to enhance opportunities for early hurricane activity, even the long-tracked Cape Verde type. Do not be surprised if June features the season's strongest storm. I am deeply concerned about the NC Coasts, particularly those struggling to recover from 2011 Hurricane Irene.
As AAM rises weather systems will become increasingly progressive. This means more frontal passages which will increase opportunities for rainfall compared to recent summers. Watch in June for a crazy hot period that is followed be a tropical storm/hurricane or a prolonged period of heavy tropical sourced rainfall.
Overall, I expect the summer to feature normal to above average precipitation.
East Coasr Weather Warriors are salivating at the thought of a weak El Nino during Winter. It means cold with excessive amounts of snow particularly in areas that are were buried in 2009-10. If any major high latitude volcanic eruptions occur in the coming months then the stage would be set for an expensively cold season.