La Nina Returns?

NOAA has put out a La Nina Advisory for the 2011 winter season. That's right folks, La Nina appears to have re-developed and is here to stay a bit longer than first thought.

What exactly does La Nina mean, you may be asking? It essentially is a cooling of Sea Surface Temperatures (SST) in the central and eastern portions of the tropical Pacific Ocean. The set up has warmer than average SST's over the western Pacific and cooler than average SST's in the central and eastern Pacific. La Nina typically occurs ever 3-5 years but consecutive episodes occur nearly 50% of the time, according to the NOAA Climate Prediction Center. While La Nina stems from the anomalies of SST's, its impacts go way beyond ocean temperatures.

Sea Surface Temperatures showing a cooler eastern Pacific which signals a La Nina return. Via NOAA CPC.

Winter of 2010 in the United States was a record-setting one. High snowfall totals lead to record Spring flooding and severe weather that was off the charts! The exceptional drought that is on-going in the South...yup, put that one on La Nina. Wichita Falls, TX became the first location with 100 days at or above 100 degrees this year! So the news that La Nina has reformed does not offer much in the way of relief.

What can we expect for winter 2011? Average La Nina winters cause wetter than normal conditions here in the Pacific Northwest and can often expect cooler than average temperatures, too. La Nina doesn't offer much drought relief during the winter months either for those in the South and Southwest,

“This means drought is likely to continue in the drought-stricken states of Texas, Oklahoma and New Mexico,” said Mike Halpert, deputy director of the Climate Prediction Center.  

 

Typical La Nina setup

Beyond the upcoming winter, it is tough to tell just how long and strong La Nina will be. Should it last into next Summer, it could mean another active hurricane season. During the 2010-11 La Nina conditions, forecasters predicted a very active tropics with 14-19 named tropical storms. As of today, we are sitting at 14 named storms this season. Pretty good, huh? With those cold waters in the Pacific, oceans try to balance out by warming up the tropical Atlantic waters to above average temperatures. So, if La Nina lingers around for another Summer, things could be active again.


With La Nina's anticipated return, records could fall again this winter. That would not be welcome news to most.

Tropical Patterns

Katia has reached major hurricane status in the Atlantic. After Irene lashed the Carolinas and skirted the Northeast, Katia has a lot of east-coasters holding their breath. As Katia formed, I had mentioned that the storm track appeared to take it out to sea and avoid being the second storm to hit the east coast in a month. So far, so good. Here are computer models for Katia's track.

All models have the storm re-curving out to sea. However, a common issue with tropical forecast is that a forecaster may wind up "riding" the models and forecasting what the computers spit out. When it comes to tropical forecasting, patterns almost work better than guidance.

Gut feelings often can be the best forecasting tool, assuming you have knowledge of the situation. Now, being from the Pacific Northwest, I obviously have little knowledge of topical histories. But having picked up a few hints along my studies have helped me to generate some opinions about the 2011 tropical season. My gut instinct was that Katia would curve out to sea. Here is why I stated that.

Take a look at Katia's actual track below.

Let's take a look at where Katia formed. Katia got tropical depression status at roughly 26 degrees West latitude and a day later was a tropical storm at roughly 33 degrees West latitude. So Katia formed rather quickly off the west coast of Africa. Through historical observations made, it has been determined that 90% of all tropical cyclones that develop EAST of 35 degrees West latitude will RE-CURVE off to sea. That is the exact situation we have with Katia. This was my first clue.

My second clue came through a process called teleconnectoins. Meteorologists use teleconnections in order to "anticipate" what may come down the road for a specific location but is used in the most general sense. The basics of this is this: what is occurring in the western Pacific (off coast of China/Japan) will occur on the U.S. east coast roughly 6-10 days later. Nothing is specific, it just assumes general trough/ridge patterns. Teleconnections can help forecast the track of a storm brewing in the Atlantic. When Katia formed, I took a look at what was occurring in the western Pacific. A trough was located just off the coast of Japan. So I inferred that this trough would generally move eastward and ultimately pull Katia out to sea when she wanders towards the U.S. coast!

I've been told it's better to go down on your own forecast than someone else's. So I decided to own my gut instinct and say what I thought; Katia will miss the U.S. and re-curve out to sea. I'm more than happy to live and die by my own forecast. That was a valuable advice given to me by one of my teachers whom I greatly respect.

Looking ahead, we have a new tropical disturbance developing in the east Pacific. Invest-95 has a high probability of becoming a tropical cyclone. Let's compare the track of Katia to that of Invest-95. 

Invest-95 has formed a little south of Katia's track, and is forecasted to track a bit north of Irene's path. Lots of time however for Invest-95 to change, so I'm not making a call on this yet.

Hello, Irene

Here we go! Hurricane Irene has taken shape and developed into a category one hurricane. Irene has already pounded Puerto Rico with strong winds and heavy rains that have left some 800,000 people without power.

At its current location, Hurricane Irene is traversing the most hostile location for a storm. The islands of Puerto Rico, Haiti, Dominican Republic and Cuba are all road-blocks for any tropical system that passes them. Their mountainous terrains threaten to rip apart the structure of any well developed storm. Just a month or so ago, Tropical Storm Emily found this out. Emily wandered into Hispaniola and was all but destroyed by Haiti and the Dominican Republic.

However, with Irene, we have a different and more dangerous situation playing out. Irene has taken a more northerly track as a tropical storm. It has just brushed Puerto Rico and during that time strengthened from a Tropical Storm into a Hurricane. What stands in Irenes' way now? Below, current National Weather Service track has it moving northwesterly, its next stop in the Bahamas.

Current models back the NWS forecast. A big blocking ridge over the central U.S. will prevent Irene from moving west in the Gulf of Mexico. A trough over the mid-Atlantic will allow Irene to cut a path along that trough and "feel" its way into making a South Carolina landfall.

This forecast track will keep Irene away from those big islands in the Caribbean and allow the hurricane to move over very warm waters. The warm waters act like fuel to the storm and will allow it to develop and intensify. In fact, the NWS is currently showing Irene making landfall as a major hurricane (in order for a storm to be classified as a "major hurricane", wind speeds must reach 110mph or greater).

A lot can happen between now and Irenes' landfall, which is sometime Saturday morning. Models are changing hourly for this storm so it will be important to keep an eye on the changing conditions. But for the first time since 2009, the United States is looking at our first serious hurricane landfall!

Emily Taking Shape in the Atlantic?

It is a long ways out (meteorologically speaking) but a great tropical system is about to take shape in the tropical Atlantic. Long range models are showing a well-developed center of low pressure forming and making landfall on the southern tip of the Florida panhandle. This storm, should it become a tropical depression/storm/hurricane will be the 5th such storm this season. Storms are named once they reach a Tropical Depression status with a distinctive closed circulation. Should this disturbance reach that stage and from all indications it will, Emily will be its name!

What kind of shot does Emily have of actually making a U.S. landfall? Let's take a look.

Here is a look at the precipitation forecast from today that is valid for this Thursday. Notice the high precipitation forecast down in the Caribbean near the Dominican Republic. By this point, Emily should be at the least a Tropical Storm. The wild card to development is whether or not the storm makes landfall on Hispaniola. If it does, Emily could be torn apart by the friction of the land. But hurricanes don't like to be on land, so sometimes a storm will shift its path to avoid land and actually just skirts right around it. If that happens, the storm will have more chances to intensify in the warm waters.
This forecast is valid for Saturday morning. Clearly the model is showing Emily making landfall in southern Florida. But is there a shot that Emily misses the Unites States entirely and just swings out to the open Atlantic? Of course, but the "steering mechanism" reinforces a U.S. landfall.
The 500mb map shows us "roughly" where systems will go. Two things to note in this map, valid for Friday. One: The high pressure over the a bulk of the South. Circulation around the high pressure is in a clockwise patter. You can visualize air moving around the central area of high pressure. Winds will "pull" Emily onshore, giving us the landfall the models have shown above.
The second point is the ridge of high pressure that is building up in the New England area. This is critical to storm intensification. Higher pressures to the north means lower pressures to the south and that helps deepen the low that enters the Caribbean/Gulf of Mexico region. These two points back up the prediction of Emily making an intense landfall.

But just a few days later, things appear to change. This map is valid for next Monday, a week out. The high pressure region over the South has disappeared, due to Emily interacting at close range with the high pressure area. Along with the weakening high pressure, a trough just off the N.E. Atlantic coast has developed. Notice the wind barbs are showing a westerly flow. Emily will "feel" this trough and hitch a ride with it. Eventually, Emily will be pulled out to the Atlantic.
The precipitation map valid for next Monday does show Emily moving back over Atlantic waters and a rapid weakening of the storm will continue. The evolution of Emily will depend on several things, most of which I have mentioned. Land and intensification play roles, but so does storm speed (fast or slow moving) and water temperature. Nearly 7 days out however, Emily may become the first named storm in nearly 2 years to make landfall in the United States!

Waiting For Arlene

Many of you may not know who Arlene is. That's ok, she was overshadowed by some of her more famous sisters. She last showed up in June of 2005. She came to the Southern U.S. from Honduras and killed a person. She was the first of her kind that year, many others followed and did far worse things.

Of course I am talking about Tropical Storm Arlene. She made landfall about 6 years ago to the date. For a tropical storm, she was a large one. Just missing hurricane status. But she ushered in one of the most active and historic hurricane seasons on record! Her more famous sisters are known as Hurricane Katrina and Hurricane Rita. There were 26 named storms in 2005, so many that we ran out of names and had to use names from the Greek alphabet for the remaining storms.

2011 tropical season is underway, it began June 1st. So far, the Atlantic basin has been quiet. But forecasters have warned that it will not remain that way as the season progresses. The Climate Prediction Center says the Atlantic will see 12-18 named storms, 6-10 of which may reach hurricane status (sustained winds over 1 minuet that measure at least 74 m.p.h). Of the named storms, the CPD says that 3 to 6 of them may become major hurricanes (Cat. 3 or higher, winds at least 111 m.p.h.). This would equate to what is referred to as a "hyper-active" hurricane season. 2005 definitely qualifies as a hyper-active season, and we just endured one last year. 2010 was an active, yet rare year. 19 named storms in the Atlantic and NOT ONE of those storms made landfall in the U.S. This is very rare.

Your probably asking yourself, "How can they forecast an entire hurricane season when they can't even predict the weather 36 hours out?!". There are signs but before I talk about those that are scientific, I want to just brush over a little research I did.

The U.S. has had a wild Spring. A record amount of tornadoes and severe weather in general across much of the country has us praying for that Summer weather to give us a break. I decided to look at past Springs and the amount of severe weather and compare it to the following Hurricane Season.

Last year, we had 1,543 reported tornadoes. As I mentioned above, 2010 had 19 named storms but none made landfall. 2009 had 1,305 tornadoes and nine named storms (1 landfall). 1,685 tornadoes were reported in 2008 and we had 16 named tropical storms that Summer (3 landfalls). 1,102 tornadoes and 15 named storms (1 landfall) in 2007. 1,117 tornadoes and nine named storms for 2006. Our active hurricane season in 2005 (26 named, five landfalls!) only had 1,262 tornado reports. Finally, 1,820 tornadoes were reported in 2004 with 15 named storms (three landfalls). Breaking down the stats, it is somewhat difficult to draw correlations between active Springs and Summers. So far this year, there have been 1,482 preliminary tornado reports. Those haven't been all confirmed yet. But still a high number. What will that translate into for this Summer?

Let's talk about trends that DO correlate to an active tropical season. We will begin with sea water temperatures. Warm water is "fuel" to a hurricane so the warmer the water, the better a chance to get storms to fire up and strengthen. The Atlantic waters are impacted by what happens off of our coast here in the Pacific. Our cool Spring can be credited to the cool, La Nina conditions. The La Nina typically gives us cooler than normal ocean waters here in the Pacific. The main goal of the ocean is to balance itself out. If we have a cold Pacific, the oceans will make up for it by having a warm Atlantic. Warm waters in the Atlantic means a good amount of "fuel" for storms this Summer!

Warm surface waters mean provide the atmosphere with a lot of uplift. When the sun strikes the warm waters and warms the air around it, that air will begin to lift. And guess what lift means for storms? You got it! Rising motions in the atmosphere help aid hurricanes and all storms for that matter! Now we have warm waters in the Atlantic and that means plenty of uplift for our storms.

Here is a map of 2010 and the storm tracks of those 19 storms that Summer.
Note how many made their way into the Gulf of Mexico. As only one storm tracked into the Gulf, that could mean a lot of untapped energy will remain for this hurricane season. As a tropical storm or hurricane makes its way through the warm Gulf, it feeds off the warm waters. When that warm surface waters get used up, the ocean pulls up cooler water from below to replace that warm water. The more storms that track through the Gulf, the less fuel for the next storms to use. With only one storm moving through that area last year, that could mean plenty of leftover energy just waiting to be used this year!

So there are the "proven", scientific reasons as to why we could see a very active, fun but dangerous 2011 Atlantic Hurricane Season.