Tuesday, April 24, 2018

An updated look at the 2018 Atlantic hurricane season, and first look at Summer.


The Atlantic Hurricane Season runs from June 1st through November 30th.

Sea Surface Temperatures (SST):

The sea surface temperatures in the eastern tropical Pacific are still cooler than average.  Things are similar in the Atlantic Basin. The eastern Atlantic off the coast of Africa is cooler than average, while the western Atlantic, Caribbean, and northern Atlantic are warmer than average.






 Four above images courtesy of WeatherBell Analytics. 

El Nino Southern Oscillation (ENSO):

The ENSO plays a huge role in tropical cyclone activity in the Atlantic basin. The question many are asking is will we see La Nina, El Nino, or neural conditions in the tropical Pacific?  The 2017 hurricane season featured a weak La Nina, as a result last year's season was twice as active compared to average.  While the Sea Surface Temperatures ( SSTs) in the ENSO zones 1/2 and 3 are cooler than average; we have seen SSTs start to rise over recent weeks.



Above images courtesy of the Climate Protection Center


 

Atlantic Multidecadal Oscillation (AMO):

Looking at the SSTs in the Atlantic. The AMO is in a transition, looks to be turning into a negative phase. Typically during a negative phase tropical activity in the Atlantic Basin is lessened. This is because the SST in the Main Development Region (MDR) are cooler. But there have been exceptions. Last year was a hyperactive season. But most of the tropical cyclones formed outside the MDR.  This could be the same for this season, because those cooler SSTs off the West Coast of Africa are cooler than average.

 Analogs:

1951,1954, 1975, 1984, 1986, 1996,1997, 2006, 2014.

These are the analogs I came up that resemble the current conditions with respect to SST, geopotential height and sea level pressure patterns around the world. 1951 and 2006 are the two closest matches.

I think we're going to see the La Nina conditions make a transition to an weak El Nino, most likely a El Nino Modoki. El Nino years typically result in fewer tropical cyclones forming in the Atlantic Basin. But a Modoki is different. Instead of forming in the eastern Pacific it forms in the Central Pacific. This subtle difference allows for a higher storm frequency, it also appears to increase the odds for Tropical Cyclones impacting the Gulf of Mexico.

Accumulated Cyclone Energy (ACE):

ACE is a mathematical formula that is used to judge how much wind energy will be available for tropical storm development for the entire season. The higher the number the greater the chance for increased hurricane activity and stronger hurricanes.  Basically ACE is a blend of the number, strength and duration of tropical cyclones , in an effort to determine how destructive the season could be.  2017 ended up with an approximate ACE of about 226. Here is a chart showing the top 10 ACE Atlantic hurricane seasons.
 

Based on my thoughts of a weak El Nino or Modoki forming by the heart of hurricane season ACE will be much lower than last year.   50-85 is my call.

End Result:

As far as Impact, last year we had a very active year with 17 named storms, 10 hurricanes, 6 major hurricanes  As I said in last year's tropical outlook, the US coast saw several landfalls , Cindy, Emily, Philippe and Nate, including two major hurricanes Harvey and Irma.
 

For 2018 things shouldn't get as intense. But we're going to still be at risk of tropical cyclones in the western Atlantic and Caribbean.  I think the East Coast will be at less risk than last year for tropical impacts, with many of the Atlantic storms staying east of the US East Coast. But for the Caribbean into the Gulf of Mexico there will be a greater risk for tropical mischief, due to my thoughts on a Modoki El Nino developing.

The number of named tropical cyclones will be 10-13, 5-6 will become hurricanes, 1-2 will become major hurricanes (category 3,4,and 5). There will be a risk for 1-2  US land falling storms especially in the Gulf of Mexico.

Names for the 2018 Atlantic season are: Alberto, Beryl, Chris, Debby, Emesto, Florence, Gordon, Helene, Isaac, Joyce, Kirk, Leslie, Michael, Nadine, Oscar, Patty, Rafael, Sara, Tony, Valerie, William.
 

Summer thoughts:

It was a cool spring. When we look at past years,  Temperatures that were below average in April lead to cooler than average Mays. The current pattern would support the validity of that idea.

PDO:

The warmth off the West Coast will help promote a ridge over the west and a trough in the East.

When we look at the analog years, they would suggest temperatures in the Northeast  would be average to slightly below average for the June through August timeframe.  At the same time precipitation amounts would be average to slightly above average.

 

Soil Moisture is above average for this time of year.  All the moisture will give us a nice buffer when we enter Summer.  High levels of soil Moisture tend to lead to less heat waves.

 

I don't think it will be an excessively hot Summer with severe drought problems in the Middle Atlantic and Northeast.

Things very well could turn cooler for the end of September into October.