Average 20 year old weather nerd. Plymouth State University Meteorology, Class of 2018. Interning this summer at NWS Boston.
By: MAweatherboy1 , 11:19 PM GMT on March 31, 2014
With March nearly behind us, and the seemingly endless winter of 2013-2014 slowly releasing its grip on the country, we are now heading deeper into spring and that means closer to another Atlantic hurricane season. With the official start of the season now just two months away, I think it is time for me to release my thoughts on how the 2014 season will go. As I've said in the past, I'm not a big fan of seasonal forecasts, but I do them anyways because how can you become a better forecaster if you don't try? Anything I post here does not represent the forecast from any official agency; it's just for fun. Now then, let's get started.
As usual, we will look at all the typical factors that tend to have an influence on our hurricane season. These include Atlantic sea surface temperatures, the ENSO (El Nino Southern Oscillation) conditions, instability, wind shear, and available moisture. Last year, many of these factors seemed to point towards an above average hurricane season, and yet it ended up being one of the quietest seasons in many years, with no major hurricanes forming and only two hurricanes, though we did manage 13 named storms, most of which were weak. So this shows how difficult it is to do a seasonal hurricane forecast. Nonetheless, I will come right out and say that just as everything looked very favorable last year, it looks equally unfavorable this year for tropical cyclone activity. The biggest factor that everyone likes to look at is the ENSO phase. ENSO refers to sea surface temperature anomalies in the equatorial Pacific region. Warmer than average waters (sustained greater than 0.5C above average) are known as El Nino, with cooler than average waters (sustained greater than 0.5C below average) called La Nina. In general, El Nino promotes increased moisture and convection in the East Pacific region, while the cooler waters of La Nina tend to inhibit East Pacific convection. These factors also influence trade wind patterns in the Caribbean Sea and the tropical Atlantic, with El Nino typically producing stronger trade winds (shear) and La Nina causing lighter trade winds. For this reason, El Nino years, such as 2009 when we had our last El Nino, tend to be below average in activity, while La Nina years, like the very active 2010 season, tend to produce more storms. We have been marred in neutral conditions for around three years now, a very long time to go with neither La Nina or El Nino. It appeared at least a weak El Nino event was coming on in 2012, but that abruptly faded, and we have been in a cool neutral for much of the past year. Things are finally changing, however, with extremely warm sub-surface water in the key ENSO regions thanks to the passage of multiple strong Kelvin waves through the Pacific, which enhance these warm pools of water (anomalies up to 6-7C above average in spots!) This warm water is now making its way to the surface, and the surface waters are responding with a steady trend towards the key 0.5C threshold, though water temperatures must sustain themselves there for some time in order for an official El Nino to occur. I have been slow to jump onto the El Nino, but it's obvious at this point that it's coming. I remain against the idea of any kind of "super El Nino" like in 1997, which saw extremely warm anomalies in the Pacific and a consequentially quiet Atlantic season. I would expect a moderation in the warm subsurface waters as they continue to rise up, and my current thinking is a moderate El Nino, peaking with anomalies around 1.0C above average sometime early in the fall, possibly with a rapid collapse towards La Nina as we head into next winter, though that is a long way off. So while I ended up going into more detail than I wanted to on ENSO, the point is that the likely formation of El Nino this year will impact this hurricane season in a negative way.
Figures 1 and 2: ENSO regions 3.4 and 1+2 are steadily trending towards El Nino.
Next (and much more briefly than that unintendedly long ENSO discussion), Atlantic sea surface temperatures. The Caribbean Sea has been running above average for SSTs, so that may be a place to watch for early season development before a full fledged El Nino sets in. Otherwise, it's an unfavorable pattern, with SSTs in the "main development region" of the tropical Atlantic running below average. I anticipate a very quiet "Cape Verde" season. Some people have pointed towards a large pocket of warm waters north and northeast of the Caribbean Sea, from a few hundred miles off the US East Coast and extending through much of the sub-tropical Atlantic, as a possible breeding ground for tropical cyclones this year. I wouldn't be surprised at a couple of frontal developments in this region, but in terms of purely tropical systems that may move west towards the US, I would say the odds of that aren't much better than in any other year, because you still need a trigger mechanism besides the warm waters. So all in all, SSTs are a negative, with the possible exception of the Caribbean Sea.
Shear, instability, and moisture: I lump these together into basically one category because they are factors that tend to change more quickly than the ENSO or Atlantic SST patterns. Shear and its causes and impacts has already been discussed at length, so just to reiterate, I would expect generally above average shear for most of the Atlantic basin all season, particularly towards the peak months and later months as El Nino develops. This will tend to limit activity. Instability has been a limiting factor in the tropical Atlantic for a couple of years now, which to me is really becoming an interesting story that is not getting the attention it should. While we're still two months from the start of the season, looking at the instability chart so far this year, it is not a pretty sight if you want activity. Instability is consistently running well below average in the tropical Atlantic, which I am confident will hamper the Cape Verde season.
Figures 3 and 4: Tropical Atlantic vertical instability is running well below average, while shear has been above average, both unfavorable conditions for tropical cyclones.
Finally, moisture. With El Nino tending to focus convective activity in the East Pacific, the Atlantic and Caribbean tend to be starved of moisture during these types of years, decreasing the odds of tropical cyclone formation. The Saharan Air Layer (SAL) is another factors that can bring dry air to the Atlantic, as dust storms roll off west Africa and into the Atlantic, killing any tropical waves that attempt to penetrate the outbreaks. A major SAL outbreak at the end of July and start of August last year may have been the first indicator that last seasons' forecasts would bust terribly. SAL is hard to predict in advance, so with my expectation for moisture to already be below average, I would say any SAL outbreaks would only add to the problem. So lack of moisture is another negative factor.
The factors I've mentioned above aren't everything; there are other factors, some of which are short term and others long term, which I haven't discussed and in some cases don't know nearly enough about to discuss. Nonetheless, this is a pretty good overview of a lot of things that are looked at in making a hurricane season forecast. So now for my numbers, which will serve as my one and only seasonal forecast for the 2014 Atlantic hurricane season, regardless of early season trends.
* 9 Named Storms
* 3 Hurricanes
* 0 Major Hurricanes
Forecasting this to be the second year in a row with zero major hurricanes was not an easy call to make, but if I am really going to go by the factors I've just discussed, I think that is the best forecast possible, as there is really nothing that points towards an active season this year, and I have already stated that I think this could be one of the least active seasons in decades (possibly paving the way for a much more active 2015 season if El Nino collapses in the winter). Simple statistics would say we should certainly have a major hurricane this year, but unfortunately that's not how the atmosphere works. Now for some other notes:
Where to look for storms- If we're going to get anything of substance this year, I would say look to the Caribbean early in the season. Water temperatures are above average, and shear isn't too bad yet and may not be for just long enough to get some activity going before El Nino becomes too overpowering. The MJO will have a say in this for sure, as if we can get a strong pulse in June or early July we could get an early storm or hurricane in that region. Next, I would say look to the more mid-latitude areas, as we will likely see 2-4 of our named storms come from non-tropical origins like old frontal boundaries that could spin up tropical storms over the above average water temperatures in the subtropical Atlantic.
Cape Verde Season- As I've already alluded to, I'm expecting an extremely weak Cape Verde season, likely with no major hurricanes for the second year in a row. We will probably see one or two storms like Humberto from last year, but nothing more as tropical waves will struggle with shear, cool waters, and very low instability. The only caveat is that if a healthy wave can survive to what may be a more favorable environment in the Caribbean, that will have to be watched. In terms of steering patterns for any Cape Verde storms that do form, it's just too early to say. Last year, it looked almost certain for many months that strong ridging in the Atlantic would steer storms farther west towards the US, only to have a last minute pattern shift and set up a strong recurve pattern, not that it mattered much with only one Cape Verde style hurricane in Humberto.
When to look for storms- Early in the season. El Nino will hamper activity during the peak months, but if it is delayed until late July or August, we may get some storms in the Caribbean. Otherwise, non-tropical origin developments can occur during the entire season, and of course we look to the August and September months for our Cape Verde storms, but my prediction is for these months to not be very active this year as El Nino sets in. The final storm of purely tropical origin will probably form no later than mid October, so it'll likely be an early end to the season as El Nino peaks.
General warning and final disclaimer- Once again, just to make it painfully obvious, these are my forecasts and in no way associated with NOAA or any other official agency. Remember also that no one can forecast before the season as to whether any storms that may form will track. The best advice is to always have a plan. If you live in a hurricane prone area of the US coastline, you will very likely have to deal with a hurricane impact at some point in the future, whether it be this year or ten years from now. Be ready!
Thank you for reading! I look forward to another season of tracking Atlantic tropical weather here. Have a great week!
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