Hurricane Season Just Over a Month Away!

Hard for me to believe, but we're steamrolling toward the start of another hurricane season. June will be here before you know it, and speculation about what type of season we will see is of course in full swing. The consensus seems to be for a near to slightly above normal year in terms of the number of named storms, though expected by most to be one of the quieter seasons we have seen in recent years, which of course have tended to produce more storms, or at least have more swirls named. The two big reasons citied for this are 1) cooler water in the Atlantic, and 2) a possible shift toward an el niño pattern.


The cooler water in the Atlantic should not surprise anyone, as we have had two years of la nina (though it rested last summer) hammer away at it. For those not aware of this, la nina tends to, over time, spill over into the Atlantic and result in stronger trade winds which can cool the waters of the tropical Atlantic. I have posted an image below of years at this time which followed two years of la nina (using the MEI, which is always my measure of ENSO) to show the tendency toward this cooler tropical Atlantic.















Compare to actual SST anoms shown here:

http://weather.unisys.com/surface/sst_anom.html

Now, given that we do not appear to have entered the long term negative AMO state yet, and the fact that la nina is fading away (or arguably has faded away), the waters could easily recover some, so this is not the end-all factor to look at here. In fact I'd be surprised if they don't recover some in the next few months, but probably not nearly enough to compete with the warmth of the waters in many of our super-active years.

This leads us to the ENSO state. A lot of models are on board with a move toward el nino as we move through the next few months, and the SSTA link above shows some warmer waters starting to show up in the tropical Pacific already. But it isn't always the actual ENSO state that is important, but rather, which way the trend is going. For example, the shift out of a nina pattern can be led by the atmosphere itself, meaning some nino-like characteristics can be present before an actual nino is seen or declared. Thus, in some cases, a weakening nina can have similar effects as an actual nino. So, regardless of whether or not we go into an official nino by later in the hurricane season, these factors would seem to support less activity than what we have averaged this decade (even removing the massive 2005 season total). The farther we get on the nino side of the spectrum, the less activity I'd expect. I'm not sure we move far enough into a nino to get a year quite as quiet as 2006 though, as somewhere between warm-neutral and weak nino seems a better guess to me right now (MEI somewhere in the 0.2 to 0.6 range?). In addition, it is worth pointing out that all these guesses as far as number of namded storms is kinda pointless in a sense, as it only takes one big one to make the season memorable, and really, it is very tough to pinpoint where storms will go, as they depend on the pattern present at the time of formation, so no matter what, everyone needs to always stay prepared if you live near the coast. The consensus of 11-13 named storms from most outlets I have seen is pretty tough to argue with though.

What could allow for more activity? Well should the waters warm more solidly and the atmosphere jolt back toward la nina, then we could see more than the consensus calls for, so that is where to look in the next couple of months. Typically it is late spring / early summer when ENSO "decides" its course.

Vacation Done... Back to Weather

The worst part about vacations is that they have to end. I think I found my new favorite city in Zurich, Switzerland. What a fabulous place, from the scenery, to the easy access to public transportation, and just an all around good place to relax. Rome was nice as well, and even though I'm not Catholic, being in the Vatican as the Pope delivered his Easter Sunday message was quite an awesome experience.

It helped that the weather was absolutely beautiful... very warm with sunshine every day we were there. In fact, temperatures were running a good 12-15 degrees above normals on most days. We expected to need a sweater and light jacket on some days based on normal temperatures for time of year, but that wasn't the case at all (and no I had not spent a ton of time trying to forecast what it would be like haha).

But now things are back to the normal routine. It looks anything but "normal" though in the eastern U.S. this weekend into early next week, with a very impressive (for late April) surge of warmth that will bring a chance for at least a couple of days of 85-90 from the Carolinas all the way up to perhaps Boston. The good news is that this time of year does not bring much in the way of humidity, so it won't be as bad as the same temperatures in say, June through August. Still, highs 15-20 above normal for the time of year is pretty warm, so for those of you living in these areas, enjoy your early taste of summer!

Vacation Time!

Haven't posted in awhile, as I've been preparing for my vacation to Europe. I will depart later today and return next weekend. Fortunatley the weather where I am going looks mild, albeit cooler than I'm used to this time of year down here in Texas.

Last week's severe weather event (talked about last time I actually posted) went about as planned. It just was not the setup for a major outbreak. Maybe I'll do some case studies or something at some point in the future as far as some key things to look for, for those who aren't already aware.

We had some wild stats from the Plains the other day. Gage, OK had a morning low of 14 Tuesday, but rose to 82 in the afternoon! Try dressing appopriately for that kind of day!

Anyway, I don't see a major outbreak of severe weather on the horizon the next few days, but some smaller scale events are possible per SPC's discussions. We may have to wait for the end of the month or early May for a more favorable overall synoptic setup, assuming continued progression of current Madden-Julian wave. These waves will also help play a role in the state of ENSO in the coming months, which of course has big implications on summer and even next winter (yes I know many are already wondering about that!).

I'll be back to posting after my trip.

Severe Weather Update

I don't have a lot to change from yesterday's thoughts as far as the overall gist of the current severe weather situation. This just isn't looking like a major outbreak of tornadoes to me, which is a good thing of course, but again, does NOT mean you let your guard down if you are in the risk areas. I have posted the current radar (as of this typing) below, and you can see a lot of storminess already out there. Moisture is sufficient as is shear, but the oreintation of the trough incoming is not prime for a huge tornado producer in my view (see yesterday's post), and you can already see the linear nature of the storms in Mississippi. We'll have to watch for any isolated storms ahead of this line, along with spin-ups in any bowed out sections or breaks in the line. Damaging straight-line winds will certainly be a threat with these storms. We also have a lot of activity in Florida, with some threat for tornadic cells, though I would think with the clustered nature, straight-line winds would be more of an issue as well. So all in all, the categorical risk on the SPC map below looks good now that they've cut back on the moderate risk some, though I still think the probabilities for tornadoes may be a bit high, with risk for damaging wind gusts perhaps not high enough in the moderate risk zone. It's been a neat storm to track, and hopefully no one will get a major hit here out of this.

Should be more threats to monitor in the South over the next week or two.

Radar, followed by SPC risk map:

Severe Threat for Tomorrow, 4/2/09

Now that we are closer to tomorrow's threat, we can hone in a little more than I did the other day. First off, check the first map below which shows SPC's risk areas for tomorrow. We still have a lead shortwave which veers winds in its wake tomorrow, and keeps the low level jet a little on the weaker side, though probably not as weak as last week's system saw initially. Still though, despite the veered LLJ, the surface winds look to have a more southerly component, which would give a decent 0-1 km shear vector, which for a tornado outbreak is the most important shear layer. I agree with SPC's moderate risk, but despite robust moisture and more than sufficient instability progged, you can color me skeptical on this being a "major outbreak" of tornadoes. I will preface this comment though by saying that if you live in the risk area, be ready! This stuff can be tricky and you don't want to be caught downplaying an event that has any potential to turn out serious.

But I will look to the past some here. The second map below is the progged 500 mb map for tomorrow afternoon. Note the strong, but sharp, and already trying to tilt negatively, shortwave headig toward the South. My reason for some skepticism is that such a pattern looks conducive for storms to fire early, and with stronger forcing due to tilt of trough, we get many storms that can more easily cluster together rather than discrete storms which in a sheared environment can be more of a tornadic problem. If you look at historical data, many (but to be fair, not all) of the big outbreaks in the south occurred with a trough that had a larger base and / or was actually more of a positive tilt variety. Why? Well, since the South almost always has a lot more moisture to work with, positive tilt means forcing isn't as strong, but still strong enough for isolated / discrete storms to fire. The third map below is from 4/7/06, which was one such major outbreak, but I could provide other examples.

In any case, as mentioned, I agree a moderate risk is warranted. I don't see it being a high risk day, or at least verifying as one at this time, and think the tornado threat will be confined mostly to initial storms in western half of moderate risk area, and then become mostly a wind / hail threat rather quickly, with spin-up tornadoes mixed in the clusters still a possibility. We're still 24 hours away though, so small scale details can still change, so stay tuned! Maps referred to above follow: