Tropical Tidbits from the Tundra

Have to go for a little while

By: Levi32, 4:20 PM GMT on March 30, 2007

Well it seems that the computer has begun to start taking over my life little by little, and my school is beginning to suffer because of it. I am therefore not on my computer until June, or maybe earlier if I prove myself, by the decision of my parents. If there's a big storm, I might be on, but I need time to do some catch-up on school. This is definitely a good thing for me, and I am almost glad my parents were wise enough to restrict me for a while. I will most certainly be back by the beginning of the hurricane season.

In case I really am gone until June, here is my first season prediction just for the records. I have had enough time to evaluate the situation this month that I am fairly confident in this forecast, but of course it is only my first one, and possibly the only one this spring.

Named Storms: 19

Hurricanes: 12

Major Hurricanes: 6

Tropical Storm or Hurricane landfalls (category 2 or less) on the US coast: 5

Major hurricane landfalls on the US coast: 2

Date of first named storm to form in the Atlantic Basin: June 3rd


I would put this last prediction in Bob's blog, but I have to go this very second so I don't have time. Hopefully you will see this Bob and if you would enter it into your contest I would be greatful. Have a most wonderful spring everyone!

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Strong La Nina? Or not

By: Levi32, 4:15 PM GMT on March 06, 2007

This is a follow-up on yesterday's discussion about the current La Nina situation. Lately there has been lots of signs, and even now visual evidence in the form of cold SSTs in the Pacific, that La Nina is on its way, and could become quite strong by the start of the hurricane season. This is certainly a valid forecast that could be made, however I want to consider all realms of possibility before drawing a conclusion. Up until now the only two things I've really discussed in relation to the developing La Nina are the SST anomaly patterns, and the lower wind shear over the Atlantic. Now think about it, is SST all that goes into the ENSO? Of course not. Surface and upper-air wind patterns play a huge part as well. When La Nina is in the workings, we generally look for less-amplified pattern. In other words, not so many huge troughs and ridges, but a more zonal jet stream pattern. This is definitely not what we are seeing as of late. My area in Alaska is a classic example right now. We have an extremely large amplified ridge to our west and a trough with deadly cold temperatures right over us and to the east. Neither of these are expected to move anywhere in the next 2 weeks (which means more boring weather for me). Strong troughs and ridges like this have been moving all around the northern hemisphere, and the pattern is by no means zonal. Another thing we look at when La Nina is present, which ties in with the zonal upper-air pattern, is the AO (Arctic Oscillation Index). During La Nina the AO tends to be positive (lower pressure over the northern latitudes and the pole), which results in a more zonal pattern. The AO was positive in January and the early part of February, but has since gone negative. The meridional pattern developing is clear evidence of that. Other indices such as the EPO (Eastern Pacific Oscillation) and the PNA (Pacific-North American Oscillation) are usually positive when La Nina is around, but right now both the EPO and PNA are virtually non-existent. The first real signs of a La Nina-like upper-air pattern will happen later this week when a large warm-up will move into the eastern US. This will be developing into a zonal warm pattern across the entire CONUS, and is more in line with La Nina patterns.

The other thing to consider is surface conditions in the equatorial Pacific. Namely, the SOI (Southern Oscillation Index). Take a look at the graph below:



Notice that the SOI has been negative since last June, but it has been trending toward neutral ever since. If this continues the SOI will soon be positive, which we normally see during La Nina, however it's not a very strong return to support the current La Nina. Having said that, here's an interesting possibility. As most of you know the SOI is the pressure difference between Tahiti and Darwin, Australia. Tahiti is an island in the central Pacific. When the SOI is negative, pressure is higher near Tahiti and the eastern Pacific, while it is lower near Darwin in Australia. Remember that when La Nina is forming, trade winds from the east are stronger than normal, which causes upwelling in the central and eastern Pacific. This is what causes the classic look of colder than normal SSTs associated with La Nina. Keep this in mind as you look at the next two images:





The Nino3 region is located in the eastern Pacific, and Nino4 is the furthest west of the 4 ENSO regions in the central Pacific. Notice that Nino3 is at -0.12 now, reflecting the current La Nina signature. However further west in Nino4, the index is still a strong positive +0.46. The island of Tahiti is located in the Nino4 region. This means that Tahiti is experiencing "El Nino conditions" in the central Pacific, since the SSTs are still above normal there. I'm thinking that this might be affecting the SOI because Tahiti isn't in the part of the Pacific where La Nina is currently taking affect. If this theory is true, then when or if the colder SSTs make it into the central Pacific, the SOI will start going up enough to show support for La Nina. La Nina may begin to take hold of this area soon, as the Nino4 index is gradually going down, despite the fact that it's still positive.

Having said all that, there is still a strong possibility of a La Nina through this summer, but it may or may not be as strong as we've all been thinking lately. The patterns and indices are just not there to support it. However we are already seeing La Nina effects in the Atlantic, so you never know. As I have said before, the ENSO is one of if not the most difficult aspect of the weather to forecast. It's a mean beast to be sure. I will be watching it very closely as hurricane season approaches.

We shall see what happens!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WUHOUND Rules of Behavior:

-No cuss words, cursing, or swearing of any sort
-No bad-mouthing others or putting anyone down
-Respect everyone and their forecasts/opinions
-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

First Offense - I give you a Warning
Second Offense - You get a timeout for 15 minutes
Third Offense - You get banned/blocked for 3 days
Fourth Offense - You get banned permanently until I or the majority of members decides that you can be un-banned

Updated: 4:27 PM GMT on March 06, 2007

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PDO, La Nina, GW, and the hurricane season

By: Levi32, 11:50 PM GMT on March 04, 2007

Note: I'm sorry this got a bit long but I just love writing about this stuff :)

Yeah I know that's a big title lol, but they all branch into each other so I can't help discussing all of them at the same time. I'll start off with La Nina and this upcoming hurricane season.

As many of you know we're entering a negative phase of the ENSO. SST Anomalies are cooling rapidly over the equatorial Pacific, as can bee seen in this image:



This signature was non-existent in early February, but has rapidly developed over the last month into what could become a strong La Nina this spring and summer. We haven't had a decent La Nina since 1999, after the '98 El Nino. Ever since then the Pacific has been in either neutral or weak El Nino conditions. However I believe this year will be different. First, SST anomalies are clearly lower than they have been since 2001. Second, the overall north Pacific SST pattern is more in line with La Nina conditions than we've seen in over 5 years. SSTs in the Gulf of Alaska are quite cold this year, and a large area of warm anomalies are present in the NW Pacific. SSTs of the U.S. west coast are also well below normal. All these are usually present during a La Nina episode.

I think the formation of La Nina is already beginning to affect the Atlantic. As soon as SSTs started to cool rapidly in the Pacific in early February, wind shear values plummeted well below normal over the entire tropical Atlantic. Wind shear in the eastern Atlantic has gone back up, but values in the Caribbean, especially the western half, are still averaging below normal. A big ball of low wind shear is migrating around the area, currently situated over the eastern Pacific, as seen in the below image:



Below normal anomalies extend all the way through the Caribbean up to north of Puerto Rico in the central Atlantic. I'm fairly sure that this is directly linked to the forming La Nina. When La Nina is present, the sub-tropical jetstream is positioned further north over the U.S.. This results in weaker upper-level winds over the Caribbean, which lowers wind shear. I believe we are seeing the beginning effects of that. These wind shear anomalies are likely to bounce back up toward normal, but I expect this tendency will continue, and could result in an early storm forming in the western Caribbean during May, depending on whether or not other factors fall in line for TC development.

Other effects from La Nina which we are likely to see in the next few months are wetter conditions in the Caribbean, and lower MSLP. When La Nina is present, high pressure forms over the eastern equatorial Pacific and northwest South America. This creates low pressure over the western Caribbean. Apart from increasing precipitation and convective activity, this pattern also directs more tropical waves towards the U.S. and Mexican coast lines. The high pressure forces most waves NW through the Caribbean, whereas during El Nino the opposite is true and tropical waves move across South America and into the eastern Pacific attracted by lower pressure there.

You can probably tell that I'm leading up to something here. I'm concerned about the western Caribbean this year. On top of the things I just discussed above, SSTs should be quite favorable and warm this year as well due to the typical La Nina pattern. Also last hurricane season the western Caribbean didn't even come close to being touched by any storm except Alberto, which wasn't even that strong. This means that there's a lot of heat and energy stored up there for this year. I am concerned that we could see a few major storms in that region this season, which could threaten the gulf coast areas of the U.S..

Global models have also been forecasting a more west-positioned Bermuda High this summer, which would direct yet more storms toward the U.S. coastline. La Nina would support this pattern as well. At this time my areas of concern for this hurricane season are long-tracked storms possibly impacting Florida and the Carolinas, and strong storms in the western Caribbean which could threaten the gulf. We still won't know where the Bermuda High will set up for 2-4 months yet, but with La Nina it's a strong possibility that it will set up further west this year.



In the image above you can see that the models are also forecasting above normal precipitation across the entire tropical Atlantic, which indicates an active ITCZ. The same models also forecast dry conditions across the eastern equatorial Pacific, which once again falls within La Nina criteria.

These signs and patterns are really stacking up, and right now I'm going with a more active hurricane season than last year, but I won't give my first "official" forecast until maybe sometime late this month.

Pacific Decadal Oscillation (PDO)

Although it is not nearly as well-known as the ENSO, the PDO is extremely important to hurricane seasons, and global climate in general. The PDO is basically El Nino/La Nina, but it involves much more than just the equator. Take a look at these images:



The image on the left side is the warm phase of the PDO, and the one on the right is the cool phase. They show SST anomalies, MSLP contours, and surface winds. These look very much like El Nino and La Nina, with similar SST anomalies in the equatorial Pacific. However there are a couple big differences that make the PDO separate from the ENSO. First of all The PDO is determined by SST anomalies across the entire Pacific, not just near the equator. The areas of the NW Pacific and the Gulf of Alaska are of greatest significance. In the warm phase, The Aleutian low is strong, and warm SSTs are present in the Gulf of Alaska. This is of particular importance to me, since Alaska is most affected by this pattern. During the warm phase there is a strong southerly flow over the NE Pacific, therefore Alaska and the west coast of the U.S. are warm and wet. In the cool phase the Aleutian low is quite weak, and cool SST anomalies prevail in the Gulf of Alaska and off the U.S. west coast. This results in a more northerly component to the flow, and a cold and dry pattern results for these areas. The PDO's climatic effects are felt primarily in the northern latitudes, with slightly less intense effects for the tropics. The opposite of this is true for the ENSO. The second reason why the PDO is different is the time scale which it operates on. Typical PDO cyles last 20-30 years, while El Nino and La Nina events only last 6-24 months. Here is a graph of the PDO index over the last century:




As you can see there have been about 4 major fluctuations in the PDO since 1900. During the 1910s and '20s it averaged slightly below normal, then in the early '20s a warm cycle began which lasted through the early '40s. From the mid 1940s through the late '70s the PDO averaged negative. It was during this time that Alaska got its reputation for being so dreadfully cold. From 1980 to the present we've been in a warm phase. Now the PDO is very similar to the ENSO, so is there a correlation between these 30-year fluctuations of the PDO and El Nino episodes? The answer is yes! Take a look at this link. From 1950 to 1976, during the PDO cold phase, there were 130 months with La Nina conditions, and only 63 months with El Nino conditions. However from 1977 to 2006, during the current PDO warm phase, there were only 63 La Nina months, and 103 El Nino months. This shows that the PDO phase has a direct correlation to which phase of the ENSO will tend to be dominant over a certain period of time. So the PDO is sort of the "big picture" of the SST anomalies over the Pacific. Another correlation is the number of hurricanes which form in the Atlantic. We all know that more tend to form during La Nina, so what about the PDO? Well during the PDO cold phase from the 1940s through the 1970s, there was a larger number of hurricanes that formed in the Atlantic than there has been during the recent warm phase of the PDO. We are now due to go back down into a cold phase, and the century graph shows that we may already be starting back down. This would provide a partial explanation for the active hurricane seasons in the last few years. So unfortunately we're headed back into an active 30 years of hurricanes in the Atlantic. Kind of like the AMO, but different.

Now I may get pummeled for this last point, but this is just what I OBSERVED, and not necessarily what I currently believe or try to prove. Take a look at this graph of global temperature for the last 150 years:



Now compare the above graph with the PDO graph. They actually fit pretty good. They both go down in the 1910s, go up in the '20s, peak around 1940, and then tank from the 1950s through the '70s. And now they're both going back up to the present. Ok, now notice something here. As you look at the global temp graph you can see that it doesn't go to like -0.4 up to +0.4 back down to -0.4 etc.. It goes from -0.4 to -0.5 then to 0, then back down to -0.2, then up to +0.4. So the waves have an upward trend to them. This is probably the effects of Global Warming forcing the entire graph upwards with time. We're coming out of an ice age, so the gradual warming is lifting the graph and the waves just follow along. Now I don't know if the PDO and global temps have any correlation, but the graphs sure do seem to fit don't you agree? My idea is that for example when there's a La Nina, upwelling occurs and deeper colder water is brought to the surface. However there's no warm water to compensate for the cold water, because the only warm water available is what was at the surface before upwelling occurred. Therefore the net gain is a cooling of the air temperature across the globe, and vice versa for El Nino. I'll have to research it more, but it's just a thought.

We shall see what happens!

Updated: 1:10 AM GMT on March 05, 2007

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La Nina Update

By: Levi32, 5:50 PM GMT on March 03, 2007



What do you see here? That's right....La Nina has arrived, and with vigor. -2 to -3 SST anomalies have been spreading from west to east and getting colder over the equatorial Pacific, and should continue to do so in the near future. We are now entering the critical period from March through May, when La Nina and El Nino generally set up for the summer. Right now I'd say La Nina has a pretty good head start. Apart from the obvious La Nina signature, the rest of the north Pacific looks more like a La Nina pattern than I've seen in a long time. For the first time in 5 years, the SSTs in the Gulf of Alaska are well below normal, which generally occurs during La Nina.

I think that this negative ENSO is already having an impact on the Atlantic, as you can see in this image:



The region of very low wind shear over the eastern Pacific has been migrating around the west Atlantic area during the last few weeks. Wind shear levels in the Caribbean have been well below normal as of late. Given the long-lasting duration of this event, I believe this is an affect that La Nina is having on the upper wind patterns across the Atlantic. Of course it's too early to speculate just yet, but this could be indicative of the pattern we will be facing during the hurricane season, with lower wind shear than we have had the last couple years. At any rate it could mean an early start to the season with a possible early storm in the western Caribbean.

Anyway, that's just a quick update on the situation. I'm going to write a more detailed post on this and the PDO either today or tomorrow.

We shall see what happens!

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MAJOR SEVERE WEATHER OUTBREAK possible over the SE today and tonight

By: Levi32, 3:56 PM GMT on March 01, 2007

Evening update 9pm eastern time:

Now that I've had some rest I can actually think lol. The absolute worst that this storm has to offer has thankfully ended now, but a substantial tornado threat still exists over Georgia, and will extend into South Carolina and northern Florida later tonight. The western most t-storm complex along the cold front has formed into a squall line, and the main threat with this will be damaging straight-line winds for the remainder of the night. The eastern-most complex in the warm sector is still producing tornadic supercells, though much less frequently than it was just a couple hours ago. These storms will roar through Georgia and the Florida panhandle during the next several hours. The threat for tornadoes will diminish gradually with time, but South Carolina could still see some isolated tornadoes late tonight into tomorrow morning before the t-storms fizzle out. The area of biggest concern tonight will be the Florida panhandle, northern Florida peninsula, and extreme southern Georgia. A strong jet max coming out of the west will be moving over the area as the night progresses, and will enhance already strong shear profiles. Also the eastward-moving upper trough will be cooling temperatures aloft, further increasing instability. Plenty of moisture and a strong low-level jet will still be around, and there will be a good chance of tornadic supercells over those areas. The cold front will push south through Florida late tonight, and will finally clear the area by the end of tomorrow. There will be a small chance of an isolated severe storm over the Florida Peninsula tomorrow, but the main event will have been long ended. As far as I know 9 people have already died to these storms today, and more than 60 injured as dozens of tornadoes wiped the SE. My thoughts and prayers go out to the families affected.

Update 7pm eastern time:

Well several dozen tornadoes have been reported so far, and 9 people have been killed; more than 50 injured. Tornadoes have been popping up like weeds across Alabama, Mississippi, and Georgia this afternoon, and that will continue into tonight. There's not much change in my forecast reasoning from below, so I'll leave all that intact. The current storms will pose a significant tornado threat well into the night, and even the Carolinas could see an isolated tornado tomorrow. That's about all I have for now. I'm flat burned out from covering all this lol! I'm taking a rest now for a couple hours. My prayers are with all the people in the path of these extremely dangerous storms. Be careful out there!

Update Thursday morning:

What a difference 12 hours can make! The forecast has greatly changed this morning, and the SPC is now forecasting a major severe weather outbreak today. A high risk area extends from the Florida Panhandle through most of Alabama and western Georgia. The GFS is now forecasting the upper trough to become negatively tilted this afternoon, with a very strong jet max racing across the south this afternoon into tonight. Shear profiles are very impressive across the board this morning, and will continue to get stronger this afternoon. The low-level jet will pump lots of moisture and 65+ dewpoints quite far north this afternoon, with 60+ dewpoints making it up into Tennessee and Kentucky. The gulf coast is now right in the mess now, and northern Florida, especially the panhandle, will get a beating as well.

Several different lines of thunderstorms are already moving across the SE. Last night 14 reports of tornadoes came in, with 118 total reports of severe weather. This morning 3 tornadoes have already been reported, and I believe we will see 2-3 dozen more before the day is out. The surface low is currently over northern Missouri moving NE. By tonight it will be situated over northern Indiana/southern Wisconsin at peak intensity, where it will sit until tomorrow and weaken. The cold front is crossing the Mississippi River right now, and will advance eastward through Georgia by late tonight. This is a very widespread outbreak. Storms are already practically everywhere. A group of tornadic supercells have formed along the Alabama/Florida gulf coast, another group is in SE Missouri, and several squall lines are traveling E and SE over Louisiana, Mississippi, Arkansas, and Illinois. Tornado watches are up for all of Louisiana, Mississippi, eastern and southern Arkansas, SE Missouri, western Tennessee, western Kentucky, southern Illinois, and southern Indiana. The situation will become very dangerous over Mississippi with the frontal passage in a few hours. Supercells will be popping up everywhere along the frontal boundary feeding off of the rich moisture from the Gulf of Mexico. These storms will move into Alabama later this afternoon, where I think they will be at their worst. By that time it will be the prime time of the day for convective development. With the trough tilt going negative, and rich moisture being rapidly advected north throughout the day, there is strong potential for widespread explosive convective development over the entire SE states.

Tornadic supercells will develop over Tennessee and Kentucky as well, and there is also potential for tornadoes over portions of Illinois and Indiana to the east of the low center where there's plenty of mid-level vorticity to start the storms rotating. Right now a line of storms along the cold front is moving through eastern Illinois, and will move through Indiana in a couple hours. The cold front will be out of Illinois this afternoon, but a second wave of storms could develop in the dry slot east of the low center. Low-top supercells are possible, and some of these could become tornadic. The cold front and associated line of supercells will move east into the Carolinas overnight tonight. Some of these storms may remain tornadic until they move off the eastern seaboard, so residents there should be ready for some decent storms. Lifted index values won't be terribly low this afternoon over the SE, but CAPE values are forecasted to be over 1000 j/kg, and mid-level lapse rates will be quite strong. All this coupled with the strong moist low-level jet, 120+ knot jet max coming over the area, strong shear profiles, and plenty of lift, should combine to produce a bad, widespread severe outbreak over the SE this afternoon and tonight. As is true with all outbreaks, sometimes the ingredients are all there, and it looks like it's gonna be bad, but then it sort of fizzles out for no apparent reason. This event is certainly no exception, and I've seen situations like this turn out to be almost nothing before. However with that said, it is highly likely that this will indeed turn into a bad outbreak, and with 14 tornadoes already reported last night, I would advise residents to pay extremely close attention to what transpires this afternoon, as things will get very very dangerous into tonight.

We shall see what happens!





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WUHOUND Rules of Behavior:

-No cuss words, cursing, or swearing of any sort
-No bad-mouthing others or putting anyone down
-Respect everyone and their forecasts/opinions
-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

First Offense - I give you a Warning
Second Offense - You get a timeout for 15 minutes
Third Offense - You get banned/blocked for 3 days
Fourth Offense - You get banned permanently until I or the majority of members decides that you can be un-banned

Updated: 2:15 AM GMT on March 02, 2007

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About Levi32

Levi Cowan has been tracking tropical systems since 2002, and is currently working on his bachelor's degree in physics at UAF.

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