Wednesday, August 22, 2018

Hurricane Lane - a Central Pacific special: August 21, Update A

Eesh. Mr. Hurricane Lane! Well the good news for today is that my on-the-ground reporter, Malia M., said this morning that the surf was pretty good on the north shore of Oahu and it was a lovely beach day today. 

But we can see that Lane is slowly creeping towards the islands. He is currently at 14.5N, 154W, and has started that curve to the north. He is heading WNW at 9mph. The overall track has shifted to slightly to the north, but there is still a large range of uncertainty so keep in mind that he could go anywhere in that cone: 

Unfortunately, he did get stronger during the day and is now a cat 4 storm  with winds of 160mph (cat 5 range: >156mph). The data is extracted from hurricane hunter planes, but his satellite imagery also supports a robust storm. We can see a really good, solid, clear eye that has been in place all day. The infrared imagery also shows a very large band of very strong thunderstorms around the eye (the red part):  

The water vapor imagery shows the overall cloud structure more clearly and we can see a good outflow (that curved 'sawtooth' pattern) on the west and north side of the storm, which is another sign of a well developed storm: 
The final clue that he is a solid storm is his vorticity (circulation), which is is also very well strong in all levels of the troposphere. I think it's almost time for an exciting <Science Alert!> on Vorticity, but before I jump into that, a few more observations on Lane and Hawaii. 

Although the track is looking a little dodgy for the Hawaiian islands and he is the strongest storms that has passed this close to Hawaii for decades, there are a few things that may reduce his intensity before he gets close to Oahu (at least):
1. There is still some wind shear between him and the Big Island. It's may keep him slightly in check, although he is strong so it won't be as big an influence as it would be on a smaller storm, but it will be something.
2. He will interact with the Big Island of Hawaii, which has mountainous terrain, which will keep him in check and may reduce his intensity as well. The outer bands have already started to cover this island, with some light rain on the southern and eastern shores:
This poor island! I can see the movie titles: Battle of The Natural Disasters! Or stay tuned for Lane versus the Volcano!
3. As he interacts with the other islands before getting to Oahu, his intensity will also be kept in check and maybe reduced. The extent of how big an impact this will have depends on how close his center gets to the other islands. 
4. Finally, his track may keep him to the south of the islands entirely - that cone is still very wide. 

If you are on the islands, remember:
1.  Run from the water, hide from the winds. This means that if you are in a place that will flood, move inland. If you are in a place that won't flood, hunker down. The greatest loss of life in a storm is from water - storm surge, flooding from rain and rivers etc. 
2. Be careful after the storm - downed power lines and water don't work well together so be careful where you walk. 
3. Get supplies for a few days (more than 3) - if you are in a place where the roads are small, they may be impassable from debris. If the power is out, then you may be stranded for a few days until help arrives. (Get some ice cream in too - if the power goes, you'll have to eat it first and it will keep you cool as well. That's my solution to many things. :-))
4. Listen to your local emergency managers - they have the best information for your locale!

Ok, now for a fun bit-o-science! Are you ready? :-) 

<Science Alert!> Vorticity: A storm has 'circulation', and it's pretty obvious what that is, right? It simply means that a storm is going around a central point, like a carousel. Well, vorticity, is essentially the way we measure the amount of circulation that a storm has. It's a very useful tool and I've used it for ages - next to a corkscrew for opening yummy wine bottles, it's my favourite (with a 'u') tool during hurricane season. ;-)

Although satellite imagery is one piece of the puzzle, the biggest clue about what sort of storm we have is the vorticity and what it looks like in different levels of the troposphere, because that gives us a glimpse into the structure of the storm. 

All types of stormy weather have a recognizable vorticity signal in the troposphere. Like a fingerprint, you can figure out what sort of storm system you have if you know what and where the vorticity is. The vorticity for low pressure fronts looks different compared to tropical storms. For low pressure fronts, the vorticity stretches out in a long line. For proper, grown-up, tropical cylones, the vorticity is confined and generally circular. 

You can also tell how strong a tropical storm is depending on how strong the vorticity is and how high into the troposphere that signal can be seen. A Tropical Storm ALWAYS has a vorticity signal that reaches the middle of the troposphere (around 500mb) because this indicates that there is some deep convection (aka big thundery clouds). <End Science Alert!>

So lets look at the Pacific and Hurricane Lane. Here is the vorticity map for 850 mb (the lowest level of the troposphere): 

You can see the signal of Hurricane Lane just south of Hawaii - the big red splodge (technical term), conveniently covered by a hurricane symbol. 
Here's the map for 500mb (the middle level of the troposphere):

In this, you can still see a nice round, red splodge in the same place as the 850mb level map. You can also see another red splodge to the northwest... but this second one isn't a hurricane because there isn't any circulation in the lower level of the troposphere. It's just in the middle levels that there is some movement.  
And here's the map for 200mb (the upper levels of the troposphere):

In this upper level map, you still see a very nicely defined Hurricane Lane vorticity signal - still orange/red, which means that there is some good circulation throughout the troposphere - we only see a signal of vorticity in this upper level if a tropical storm is actually a hurricane. And the stronger it is up here, the stronger the hurricane. Meanwhile, that other red splodge doesn't have a corresponding signal this high up. But instead, we see a lot of lines - there is vorticity up here, but it is more like low pressure fronts (troughs). 

These amazing maps are produced by the University of Wisconsin-Madison's Cooperative Institute for Meteorological Satellite Studies - and a jolly good job they do too! I'll talk about how you can access them for yourselves in a future post. 

I think that's it for now. Get ready and be prepared my friends in Hawaii! 

Twitter: jyovianstorm
These remarks are just what I think/see regarding tropical storms. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast. This is not an official forecast.

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