Saturday, August 19, 2023

Hurricane Hilary: August 18, Update A

With Hurricane Hilary out there and still heading in this direction, I've started going through my hurricane checklist... two lychee martinis later, I'm now onto the ice cream which, may I say, is quite delicious. If you are a regular reader, you may be wondering where the wine went... me too! ;-)

Before we get to what else is on my checklist, what's going on with Hilary? As expected, she intensified to a mid-size cat 4 earlier today (winds got to 145mph - cat 4 range is 130-156), and also as expected, she is slowly starting to weaken - she is a bit weaker now and is back to being a borderline cat 3/cat 4 storm with winds of 130mph, central pressure of 948mb. 

The outer bands are over Mexico:

But it's mostly rainfall at the moment, not too overly stormy (technical term ;-)). Generally, I see that the convection (rainfall) has decreased a bit and, more interestingly, the west side is not as robustly round as it was compared to the imagery from yesterday:

This is because there is dry air to the north and west, but also because there is some wind shear - this is what I was hoping to see today. Long may that continue! So what do these satellite images mean and where do you find them? I think it's time for a double feature of a 
<Technical AND Forecasting Alert!>. Lucky you! 

<Technical AND Forecasting Alert!> Satellite Imagery: I mainly use three sorts of satellite images: visible (geocolor), water vapour (spelled with a ‘u’ of course ;-), and infrared. To access these, go to this NOAA website: Click on the tab marked 'Storms' at the top, and the storm you are interested in the drop down menu. That page should load up with the Geocolor satellite imagery - the visible imagery... it is what you would see if you took a colour photo. Best used during daylight hours of course! ;-) This is useful to see the full extent of the outer bands. 

The water vapour image is also pretty obvious…it shows how much water vapor there is in the atmosphere. To find these, on the same page, on the left panel, click the tab labeled 'Channel Loops' (usually with the name of the storm as well). Bands 8, 9, and 10 are the water vapour at different levels in the atmosphere (high, middle, and low). Living in LA, of course I like looking at the moving pictures... the animation loop or animated GIF in the list of options in each channel section. The yellow/orange/brown areas are dry air (think of parched desert colours) and any other colour indicates some amount of water vapor, with green being a lot (think of well watered lawns... just like ours will be in a couple of days!). This is what the mid-atmospheric level water vapour looks like for Hilary at the moment:

You can see the dry air to the north and west quite clearly. Dry air inhibits the storm from intensifying, and an area of humidity and water vapor helps a storm to keep going. To toggle between different water vapour channels from this page, above the image, on the left side of the screen you will see a drop down menu (next to 'Band'). 

My favourite is the infrared satellite imagery because not only does it show where the storm is, but it also gives us an indication of how strong it is and what sort of weather we have. To get to these, you can pick Band 11 - called cloud-top phase (or cloud top IR).

The colours represent how high the clouds reach into the atmosphere because they are based on the temperature at the top of the cloud (which is what the satellite sees). It gets colder the higher you get in the lower atmosphere (the troposphere - I'll talk about the troposphere tomorrow). So we can tell from cloud top temperature how deep (high up) the clouds are and therefore how strong the convection is! The red colours are very big high clouds with the coldest temperatures and blues and whites are lower, warmer clouds. The redder the cloud colour, the more active the convection, the stronger the storm. My general rule of thumb (having seen these images and lived under them at the same time) is that blue and green areas are mostly clouds, with some very heavy rainfall in the green areas. But as you get to the orange and red, you get thunderstorms and possible tornadoes (especially in the red/dark gray areas). <End Technical and Forecasting Alert!>

Back to Hilary... she is clearly being impacted by dry air and wind shear, and as she continues to move north, she will be moving over cooler water and also interacting more with land, all of which will lead to a continuing steady decrease in strength. But she is still a robust storm and that eye is a beauty, showing us that the circulation is still very strong, and I agree with the NHC that she will be a hurricane when she clips the Baja peninsula - I expect she will be a strong cat 1 or weak cat 2:

She's currently at 19.7N, 112.7W heading NNW at 13mph, which is a pretty good clip for a hurricane. 

As it's a Friday evening, I'll throw in another <Forecasting Alert!> just for you for fun! 

<Forecasting Alert!> Watches and Warnings: You may have noticed that the colour of the coastline in the track chart above has changed from yesterdays lovely, fluffy, spring-like pinks and yellows, to todays bold and dark blues and reds. This is because these regions have changed from a 'Watch' (the fluffy spring colours) to a 'Warning' (the dark bold colours).

A Watch means those conditions may occur in those areas... but then again, they may not. 

A Warning means that those conditions WILL occur in those areas within the next 36 hours. 

A Tropical Storm Warning means you should expect winds of 39-73 mph within the next 36 hours, and a Hurricane Warning means you should expect winds of 74 mph or higher in the next 36 hours. <End Forecasting Alert!> 

So even if the center of the storm hasn't reached the Baja peninsula, you can see that the winds will start to pick up on Sunday ahead of the storm. 

In case you need any hints on supplies (for Greg M. in San Diego), here is my general list... 

- water
- batteries and flashlight
first-aid kit
full tank of gas in the car (or petrol if you are like me) 
- canned food and non-electric can opener
- sunscreen
- insect repellant
- hand-held fan
- candles and matches
- fully charged smart phone and laptops
batteries for the radio (if you have one)
two tubs of ice cream (different flavours to avoid boredom)
- some ice cream cones (optional)
twelve bottles of wine (mostly red – no point getting too many white if there is no power for the fridge to cool it in!),  
- a non-electronic wine bottle opener
- fixings for lychee martinis (for the fruit - very healthy)
- good books to read
- cheese
- bags of PG Tips in a ziploc bag
- more ice cream (doubles up as a source of water). 

As a storm approaches, you will need to start the day by eating up the ice cream... just in case the power goes out of course. ;-) 

More tomorrow (after I've been shopping! :-)). 

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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