‘Ocean-Atmosphere Setup’ Suggests Big 2020 Atlantic Hurricane Season Ahead

Written by on April 27, 2020 in Rest of World, Tropical, United States of America with 0 Comments

Based on all the current parameters and model projection, the 2020 Atlantic Hurricane Season is likely to be busy one. However, let’s keep in mind that although 9 out of 10 factors can align perfectly, it just takes one factor to significantly suppress development or intensification in a seemingly perfect environment, e.g Saharan dust, wind shear etc.

Remember, it only takes one storm for it to be a bad season.

Credit: Mark Vogan

Let’s start of by looking at ocean water temperature. Here are the current sea surface temperature anomalies.

Global

Credit: NOAA

Just by looking at the above, there are a few things which stand out. Note the cold mid and north Atlantic in contrast to the warm tropics and +2C above average water off Africa and within the Gulf of Mexico. Two key areas. 1st for development and 2nd for intensification on approach to US or Mexico.

The overall profile of cool down western North America and cool over warm in the Atlantic, makes for a favorable base state for development and intensification.

Tropical Atlantic

Credit: NOAA

Caribbean

Credit: NOAA

CURRENT SST PROFILE/ENSO STATE AND POTENTIAL INFLUENCE ON ATMOSPHERE

Recent years has seen the focus of warmest waters compared to normal outwith the deep tropics and over higher latitudes. So a lot of TS formation and particularly strengthening has occurred outside of the main development region. A recent warm tropical and subtropical Pacific has also meant focus of energy has been over the Pacific rather than Atlantic, typical of El Nino years.

However, this year’s setup looks much more classic for a big Atlantic year. Big year’s can also start early and there are hints of early season development in the next couple of weeks.

This years cold over warm profile within the Atlantic and cooler Pacific usually leads to higher atmospheric pressure over the cooler SST’s while lower pressure and higher humidity focuses over the warm SST’s of the main development region.

Recent years have seen an increase in westerly upper level wind shear and drier air travelling from Pacific eastwards through the Caribbean into the tropical Atlantic due to the presence of El Nino and associated warmer than normal waters off western North and South America. This has kept a lot of tropical cyclone activity away from the western Caribbean and even Gulf of Mexico.

El Nino and an unfavorable Atlantic SST profile has, along with other factors, increased the amount of African dust carried on the easterly trade winds from Sahara across the Atlantic to Caribbean. This has significantly suppressed TC formation, especially during El Nino years.

PROJECTION

At the moment surface waters of the east equatorial Pacific up against South America remain warm but stacked more to the western side of the basin.

If you take a look at the below animation, colder waters are gathering and eventually this is expected to upwell to the surface by summer. With cooling reaching the surface, the atmosphere should respond.

This cooling should bring the ENSO index to cool neutral for the heart of the hurricane season. With cooling surface and sub surface waters, this relaxes westerly wind shear through the Caribbean and allows energy to focus within the tropical Atlantic.

The majority of models have the ENSO slightly on the cool side of neutral for the heart of the season (August-September)

COULD GULF OF MEXICO & CARIBBEAN BECOME HOT TUBS FOR KATRINA, RITA, WILMA, DEAN AND FELIX-LIKE HURRICANES IN 2020?

The Caribbean and Gulf of Mexico are typically very warm bodies of water each summer which heat peaking during September, right at the peak of the hurricane season.

Every few years, these waters not only are warmer than usual but can contain deep subsurface rivers of super warm water which flow around the northern end of South America, circle Cuba and loop the central Gulf of Mexico before exiting as the Gulf Stream between Florida and Bahamas. Known as a loop current, this feature can spawn hot eddies which rotate away from the main channel and when hurricanes cross them, their unlimited ‘high octane’ heat source feeds a hurricane. As a result, they can explode from Cat 1 to Cat 5 within 36 hours.

With the level of warmth and coverage of warmth so early this year, my fear is that another series of super hurricanes could develop like we observed in 2005 and for Mexico, 2007.

DETRIMENTAL PLAYERS WHICH SHOULDN’T BE OVERLOOKED

So, very warm waters within the deep tropics, particularly within the GOM and around Cape Verde combined with a seemingly conducive atmospheric environment (Pacific-Atlantic SST profile, neutral ENSO) all point to a highly active season ahead. However, Saharan dust or the wrong phase of the madden julian oscillation can throw a spanner in the works, so a big year ISN’T necessarily written in stone.

Credit: NASA

The MJO can significantly increase or decrease the probability of hurricane formation and intensification within the Atlantic depending upon it’s phase. There is evidence within the long range models suggesting a favorable MJO for Atlantic hurricane production during the heart of the season.

Credit: weather.com

If you look at the below CFSv2 SST forecast for June through August and July through September, notice the tropical Atlantic remains warmer than normal while it has a ribbon of cool representative of a La Nina developing within the Pacific. These factors combined support favorable conditions for the Atlantic.

June-July-August

Credit: Tropical Tidbits

July-August-September

Credit: Tropical Tidbits

EARLY START TO CAPE VERDE SEASON?

Another area of unusually warm water, this early, can be found around the Cape Verde. This suggests an earlier than usually start to the season which typically doesn’t kick off before August due to waters being too cool.

However, waters are already at August strength and so thunderstorm clusters riding the African easterly jet could see development quickly this year.

All in all, I, like other forecasters, are predicting a big year in 2020 with 9 hurricanes and 4 major. The extremely warm Gulf of Mexico and even Caribbean is a big concern for strengthening right up until a US or Caribbean island landfall.

FEATURED IMAGE CREDIT: UNICEF (Damage from Dorian on Bahamas in 2018)

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