19 year old freshman at UNC Asheville majoring in atmospheric sciences. I'm deaf and proud of it :) Twitter: @KyleNoel15
By: Bluestorm5 , 3:04 PM GMT on May 03, 2014
Hey, y'all! I hope the year of 2014 is off to a wonderful start for y'all. Well, we're now in the month of May which mean the traditional start of 2014 Atlantic hurricane season on June 1st is quickly approaching. The month of May is also the best time to release a yearly hurricane season forecast as well. I know some bloggers on Weather Underground like to release their forecast a little earlier on March or April, but I prefer to release my forecasts as close to deadline as possible because of accuracy. First of all, no one should ever depend heavily on seasonal hurricane forecasts as we all found out the hard way last year. 2013 hurricane season was expected by many to be an active one with the number of storms, hurricanes, and major hurricanes to be above normal. However, we ended up with 14 storms, 2 hurricanes, and 0 major hurricane (normal season is 12 storms, 6 hurricanes, and 3 major hurricanes). My forecast last year was 14-18 storms, 6-8 hurricanes, and 2-4 majors. Technically because I got the number of storms correct last year, I was one of 15 winners out of 142 WU bloggers for trHUrrIXC5MMX's (now MaxWeather) contest. Last year, I chose to go against the consensus and predicted a calmer season. Even so, my forecast still busted horribly like nearly every tropical meteorologists, WU bloggers, and weather geeks did. The bust was so bad that the infamous Colorado State University hurricane forecasting research team nearly ran out of funds for their wonderful project that had been going for around 30 years now. Seasonal hurricane forecasts are not perfect, but that's the beauty of science. Even if we know that the forecast isn't going to be great, at least we're still trying so we can learn something new so we can become better at forecasting. As for myself, I've gotten a lot more forecasting practice since the first day of college last August. I spent about hundred days total forecasting in WxChallenge for eleven cities around this country. I did very well, finishing ranked 208th in nation out of 2,000 forecasters while winning a trophy for the best 8 days forecast for Grand Forks, North Dakota among 500-750 freshmen & sophomores. I also finished 4th out of 25 UNCA forecasters for the year as well. Doing WxChallenge forecasts almost everyday in college definitely help me become a better forecaster as well as picking up more meteorology knowledge and what to expect from computer models as well as recognizing trends from them. I am confident that doing these forecasts will help me with hurricane season forecast as well. Now that I got higher confidence in my forecasting skills, I believe I can do much better with this year's forecast than the last several years combined. Now, it's time to discuss what to expect for 2014 hurricane season in Atlantic basin.
LOOKING AT OCEANIC AND ATMOSPHERIC PATTERNS
I don't think many people realize how global the effects of oceans are to our planet's atmosphere, especially when it comes to weather in United States of America. Atmospheric patterns for certain locations on this planet heavily depends on how much warmer (positive phase) or cooler (negative phase) the oceans are comparing to normal. Meteorologists call them climate oscillations. Like the activity of almost all weather in USA, the activity of an Atlantic hurricane season depends on what the conditions are like for oscillations in several places. For this forecast, we'll focus on three oscillations: El Nino-Southern Oscillation (ENSO or El Nino), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). The most important one out of these three for Atlantic hurricane is the phase of El Nino-Southern Oscillation. During a year with positive ENSO phase (also known as El Nino event) when the water of equatorial Pacific is very warm, the air above the ocean will be warmer as well. Warm air over Pacific will rise up into the atmosphere because it's more dense than cold air. As result, we get more thunderstorms and the outflow from these storms will lead to higher wind shear across Gulf of Mexico, Caribbean Sea, and Cape Verde region of Atlantic Ocean. Higher wind shear is not healthy for tropical cyclones because it'll tilt the structure of the storm and kills it. Bottom line: El Nino events typically lead to less active than normal hurricane seasons in Atlantic Ocean. Now, it's time to discuss the current phase of El Nino-Southern Oscillation. It has been five years since we last got an El Nino event in Pacific heading into Atlantic hurricane season, the last one during the year of 2009. However, the end to the streak of non-El Nino years seem imminent heading into 2014 hurricane season. A strong westerly wind burst occurred over Pacific this past winter resulted in Kelvin wave been created in waters of Central Pacific. With an anomaly of 6° Celsius (Figure 1), this is the most impressive Kelvin wave ever observed. The anomaly of this current Kelvin wave is even warmer than the one in 1997 leading to "Super El Nino" event.
Figure 1: Climate Prediction Center's weekly ENSO update as of April 28, 2014
However, there was an episode of easterly winds during that temporarily stalled the eastward movement of Kelvin wave which lead to a stall in the warming of Pacific in ENSO region (Figure 2). Because of this, it's unlikely we'll see "super" El Nino similar to the one in 1997. However, westerly winds should resume at some point in May or June and this powerful Kelvin wave will move toward eastern equatorial Pacific. Once this wave start surfacing over there, El Nino event will start with a massive surface warming of equatorial Pacific that will release a lot of warm air into the atmosphere (Figure 3).
Figure 2: Official El Nino daily value from website TropicalTidbits run by WU blogger Levi Cowan. You can clearly see the stall during April.
Figure 3: Here's GIF of El Nino events of 80s and 90s from NOAA. Note how the warming started in eastern Pacific and spread out westward. If you can't get this GIF to work, just open this image in new tab and that should do the trick.
Now, let's move on to another oscillation: Pacific Decadal Oscillation (PDO). Why is this oscillation so critical to Atlantic hurricane season? Because having Pacific Decadal Oscillation in positive phase, when waters off coast of Alaska and British Columbia are warmer than usual, sometimes enhance El Nino to a stronger strength. PDO had been mostly negative since 2007, but it doesn't seem to be the case this year with all 3 months of 2014 showing positive number so far. In additional to that, there's a CFSv2 forecast (Figure 4) that shows PDO staying positive during this year's hurricane season as well as El Nino of at least moderate strength existing at the same time. Yet another oscillation to consider for 2014 Atlantic hurricanes season is Atlantic Multidecadal Oscillation (AMO). For most of the last 19 years since 1995, AMO had been positive resulting in few more active hurricane seasons than normal. While AMO is capable of staying positive for another few decades, it's undergoing a hiccup this year as it had turned negative in the past few months. It's negative because the water in Cape Verde region of Atlantic had turned colder than normal while subtropical waters off coast of New England region of United States of America had turned much warmer than normal (Figure 5). Waters between Canada and Europe is also much colder than normal which is yet another support why AMO is negative. Why is this so important? Because Cape Verde region is birthplace of some of the strongest and long-lasting hurricanes. Having cooler waters in that region reduce the chance of a formation of Cape Verde-type hurricane. Therefore, the number of storms, hurricanes, and majors get reduced in negative AMO years.
Figure 4: Here's the CFSv2 forecast from Climate Prediction Center for September 2014 to November 2014. Note how El Nino is at least of moderate strength while Pacific Decadal Oscillation (PDO) stay positive during this time period.
Figure 5: Sea surface anomaly from website TropicalTidbits run by WU blogger Levi Cowan.
In additional to oscillations, we could also look at Sahel region of Africa where tropical waves are produced every season. I've never thought about looking into the wetness or dryness of Sahel region determining Atlantic hurricane season until @webberweather pointed it out on Twitter back in March. The idea of using Sahel region to forecast the season: in a wet Sahel year, tropical waves are more powerful and this lead to more stronger storms for the season. Dry Sahel year, according to this theory, got an opposite effect. We have been in a period of dry Sahel region for a few decades now (Figure 6), but most of forecasts point to a wet Sahel region this time around for 2014 hurricane season which could promote at least some activity in Cape Verde region.
Figure 6: Most recent Sahel region rainfall graph from University of Washington/NOAA NCDC.
FORECASTING 2014 ATLANTIC HURRICANE SEASON
Now that I've explained current conditions of oscillations and planet's atmosphere, it's time to come up with a forecast. Obviously I want to have analogs that's the closest to this upcoming season so I got to start somewhere. Because of numerous of forecasts calling for at least moderate El Nino (value of 1.0+), I've decided to use all years since 1950 with El Nino having a value greater than 1.0. That'll give me 14 hurricane seasons to work with. In one of my atmospheric science classes this past spring semester, I found Excel to be extremely useful tool for number crunching so it's time to use my knowledge of that program for my hurricane forecast. For each of 14 hurricane seasons with at least moderate El Nino, I've added in how strong El Nino was, what was the phase of PDO and AMO that year, and whether if Sahel region was wet or not at the same time. Next, I did series of calculations using Excel to average out number of storms, hurricanes, and major hurricanes (Cat. 3 or stronger) for four different categories (strength of El Nino, phase of PDO, phase of AMO, and phase of Sahel). Now that I'm all set up with my large database, I know that this year could have a positive PDO, a negative AMO, and a wet Sahel region. Therefore, I used averages of these three categories and calculated them with averages of a moderate El Nino year, a strong El Nino year, or a super El Nino year. Based on my calculations, I came up with the average of 7.4666 storms, 3.7666 hurricanes, and 1.25833 majors if you combine all three final averages from each El Nino categories I've listed on Excel (Figure 7). It's worth noting that the average amount of storms decrease the stronger El Nino is, but it doesn't seem to affect number of hurricanes or major hurricanes.
Figure 7: Calculations that I did using an Excel spreadsheet. Database of 14 hurricane seasons with at least moderate El Nino strength included. Values of El Nino, PDO, and AMO are found using couple of sources linked. Sahel years are determined using a graph (Figure 6). Finally, calculations are done by me. Open the image in new tab for the absolute best quality.
Now I'm ready to release my forecast. The factors I looked at for this forecast included several forecasts that show this year will have at least moderate El Nino which could increase the wind shear across Atlantic basin effecting majority of Atlantic cyclones, a positive PDO possibly enhancing the strength of El Nino even farther, a negative AMO to reduce activity of Atlantic season thanks to cooler Cape Verde waters, a wet Sahel region to at least allow some stronger tropical waves to survive in Cape Verde region, weak vertical instability that should limit the strength of tropical cyclones in Atlantic, looking at analog years with at least moderate El Nino, and my Excel calculations above. Based on these numerous factors, here's my forecast for 2014 Atlantic hurricane season: 7-10 storms, 3-5 hurricanes, and 0-2 majors (Figure 8). Also based on these factors, I believe that most of activity for this year's hurricane season will be in subtropical region of Atlantic thanks to warmer than normal waters while Cape Verde region struggles due to higher shear from El Nino and cooler waters. Stronger tropical waves, thanks to wet Sahel region, should open up few windows in Cape Verde region, though. However, I am not expect for any storms to survive the infamous "Graveyard of Tropical Cyclones" of Eastern Caribbean Sea because almost none of them will be strong enough to handle higher shear that could be found in that area. While most of Gulf of Mexico should shut down due to higher shear from El Nino, northern half of the gulf could stay out of trouble and allow a strong storm or two to sneak into Southern USA (Figure 9).
Figure 8: My 2014 Atlantic hurricane season forecast.
Figure 9: My forecast of four regions where storms could peak in.
Just remember that seasonal hurricane forecasting is not a perfect science and these kind of forecasts shouldn't be taken seriously, especially my own forecast. Please pay attention to National Hurricane Center website once the season get rolling on June 1st. I wish y'all an another safe hurricane season and thank y'all for reading my long blog post. Feel free to leave any question, correction, or comment below :)
- Kyle Noël
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