Friday, July 02, 2021

Hurricane Elsa: 2 July, Update A

I know, I know, you are wondering if I fell off this planet. I have no plans on traveling into space quite yet, although I did travel across time and space and am now on the Other Side of Elsa. 

I missed Tropical Storm Danny Boy, but he was another very short-lived storm of less than 24 hours and developed just off the S. Carolina/Georgia coast a few days ago. He was a Blot on their Landscape but hopefully brought some cooling drops of rain. 

Now for Elsa who popped up a couple of days ago and is officially the first Hurricane of the season with winds of 85mph, central pressure 991mb. This makes her a mid-size cat 1 storm (cat 1 range: 74-95mph). She crossed the Lesser Antilles today, near St. Vincent and St. Lucia, as a very weak cat 1 storm and is currently at 13.7N, 62.5W, zooming along in a WNW direction at 29mph... this is unusually fast for a hurricane and is one of the things throwing the forecast track off in the longer timeframes (4 and 5 days). In the shorter timeframe, she is heading towards the Dominican Republic and as she is in such a rush, she will arrive there tomorrow. 

I think there is a possibility that she will remain on the southern side of that cone of uncertainty, so she may actually not cross any land until she gets to Jamaica. We will know more tomorrow of course. If she doesn't cross land, she will get stronger because there isn't anything preventing her intensification - she is in a region of very low wind shear at the moment and over warm Caribbean waters with the upper 100-125 m warmer than 26 deg C. 

I expect she may be a cat 2 storm as she approaches Hispaniola and, again, depending on the exact track, there is actually a chance she will blossom to a cat 3 because the waters in that part of the Caribbean are warmer. Beyond that, it depends on the track she takes and how much she interacts with the islands. When she crossed the islands earlier today, she took a little hit which we can see in the infrared satellite imagery (ooh, I think I can hear Technical Alert bells in the background!) as the convection decreased: 

It looks like she is recovering from that now and is trying to get better organized - which we can tell from the cloud structure to the north of the center because it's got that lovely outflow pattern we see with hurricanes. Her circulation is really strong in all levels of the troposphere (ooh, the sirens of a Science Alert are also in the air!! :-)) which means she is definitely a hurricane. 

<Science Alert!> The Troposphere: Our atmosphere is divided into layers - like a delicious trifle (like the one sitting in the fridge in this house right now) or seven-layer dip. In each layer the air temperature either increases with height or decreases with height. The troposphere is one of these layers. It is the lowest layer of our atmosphere and extends up from the earth (ground zero if you like) to about 15-16km in the equatorial regions, and to about 8km in the polar regions of the planet. This is the layer of the atmosphere we live and breathe in. All our 'weather' essentially occurs in the troposphere. The troposphere is defined by decreasing air temperature with increasing height. You would know this if you climbed a mountain. Or the easier option, of course, is to just look at pictures of mountains and see the snow at the top (known as the ‘Flat Florida Option’ ;-)). The top of the troposphere is called the tropopause. Strong tropical storms have clouds that reach as high as the tropopause - and in a few very strong cases, they can extend even higher into the next layer up - into the stratosphere, which is the layer of the atmosphere above the troposphere. The stratosphere is defined by air temperature increasing with height. The ozone hole is in the stratosphere. The top of the stratosphere is around 50km height and is marked by the stratopause. And the layer above that is mesosphere, where air temperature decreases with height again until the mesopause. Above that is the thermosphere, then the exosphere... and then we get to space, which is where I hear a few people will be heading later this month.<End Science Alert!>

A Science Alert! followed immediately by a Technical Alert! It is our lucky day! ;-) 

<Technical Alert!> It's really useful to know that temperatures decrease with increasing height in the troposphere. This gives us a clue about how strong a storm and it’s convection (rain, thunder etc.) is from the satellite images. The satellite imagery above is the infrared imagery and shows the temperature at the tops of the clouds. Higher cloud tops means a more turbulent atmosphere and stronger convection, but it also means colder cloud top temperatures. The red areas are the coldest cloud tops and they correspond to very heavy rain, strong winds, a lot of thunder, tornadoes… basically everything and the kitchen sink (but not the trifle). Orange areas are less strong – thundery weather, strong winds, heavy rain. Yellow would be strong winds and rain, green is mostly rain with some wind, and then it gets to light rain/just cloudy where we see blue and gray.<End Technical Alert!>

You will all be quizzed tomorrow so I hope you were paying attention. ;-) 

I think that's all from this side of the pond... I'll be back tomorrow. It's wine-o-clock here (well, it's been wine-o-clock here for the last couple of hours actually...). 

Toodle pip!




These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and local weather service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know. 


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