Alastair Thompson Profile picture
Feb 3 13 tweets 8 min read
Very Intense Cyclone Batsirai #ExtremeWeather Update 4. 3/2/21

#Batsirai has slowed down to a crawl, it has been moving WSW at 5mph (7kmh) for the past 17 hours at least. It is also wobbling and weakening. But the current official forecasts do not reflect this WRT to landfall.
This is common for an EWRC [Eye Wall Replacement Cycle], after which the storm can be expected to strengthen rapidly. #Batsirai's eye is certainly now very ragged. (images here used to verify speed and heading data). It appears the track is to the north of the current forecast.
The much larger eye indicated in the latest imagery is still full of cloud, and it appears the EWRC is complete.
Spaghetti model data shows no change to the track heading or timing, but bear in mind that the more larger/intense a cyclone is the less predictable it becomes.

Typhoon #INFA and Hurricane #Dorian are very good examples of this.
This closeup animation - 24 hours - shows the eyewall replacement cycle in close up - which is not yet complete as the new eyewall structure is far from complete. Comparing this with the track the only real variation is slightly slower forward motion than expected.
24hour Satellite Loop image of #Batsirai to 10.15am UTC today. 3rd February. Outer bands of the storm have now reached Madagascar's East Coast, current forecasts suggest landfall of the eyewall will take place at around 6am on Saturday 5th February.
This simulation animation from the GFS model shows six hourly rainfall from 6am tomorrow (4/2/21) morning to 6am Monday (7/2/21).
This plot shows the accumulated rainfall as of 7/2/21.
This animation shows latest GFS model run's forecast 10m sustained winds. It shows around 90 knots (105mph 166kmh) at landfall.
There is some good news for Mozambique & South Africa in the latest few GFS runs. These four plots showing accumulated rain as of 6am 10 Feb.

1. 1/2 6z
2. 2/2 6z
3. 2/2 18z
4. 3/2 6z

A clear trend in the GFS model has #Batsirai turning south after crossing Madagascar.
And the latest run from the European ECMWF model is in agreement on this.

All that being said, everything is dependent on what happens over the next 48 hours following this eye wall replacement cycle.
Specifically if #Batsirai:
- reorganises itself quickly and strengthens.
- continues to move very slowly, possibly weakening but generating more and more atmospheric water.

Then other scenarios become possible.

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More from @althecat

Feb 3
This is the UK-Met model's solution at 120 hours. As the AccessG model is associated with the UK-Met model (which only runs for 144 hours) for this reason I am discounting it in this scenario. The ECMWF and GFS models are the two tropical phenomena specialist models.
Here we see the ECMWF models 120-240 hour prognostication.
And here's the GFS 120-240 hour prognostication.

The main difference at the starting point is that the GFS is expecting four lows two strong & two weak and this results in a sharply different outcome.
Read 9 tweets
Feb 3
Spaghetti model simulations of several tropical storms currently north west of NZ are not looking at all good.

The possibility of a cyclone coming into the Tasman and making landfall on NZ's West Coast is now non-zero.
The above map is the European ECMWF ensemble map for the area. This specific model map is for SPO9 a designated disturbance/low pressure system of concern.

Until very recently the models had suggested it would be pulled away to the East of NZ - which is what typically happens.
In this region we have four different models (GFS-US, ECMWF-Euro, AcessG-AU and CMC-Canada) each of which has a different solution on how this will play out.

But the trend is in the direction of a threat to NZ. Each of these plots show the water/energy modelling for around 12/2.
Read 7 tweets
Feb 2
Update Thread:

#ExtremeWeather #Madagascar #Batsirai #CycloneBatsirai

Intense Cyclone Batsirai has strengthened rapidly and grown significantly larger. It has now passed Mauritius and its outer bands are now over Reunion.
Madagascar is 1000kms long top to bottom and #BatsiraiCyclone's outer bands are roughly the same size. With sustained winds of over 113 knots the storm is now the equivalent of a Category 4 Major Hurricane.
The JTWC's latest forecast track update #13 shows the storm maintaining very intense cyclone intensity up to landfall (of the eyewall - maximum strength winds) in the morning on Saturday. Rain and high winds will arrive on Friday.
Read 12 tweets
Feb 1
A satellite view over NZ this morning. Two massive atmospheric rivers are colliding over the Tasman sea and delivering rain in massive quantities over the South Island.
Zooming in to the satellite imagery we can see that this stream of clouds is a massive area of convective thunder storms sweeping in from the North.
And if you zoom in ven closer you can see these thunderstorms are crossing the Southern Alps from the look of things. [see,…] for live images.
Read 10 tweets
Feb 1
Here's your problem Kiwis. A persistent atmospheric river running for the next 111 hours across most of the country.
And after that you may or may not get hit by a moisture laden Northerly Storm/Cyclone.
16 day atmospheric water forecast.

You can chalk this up to #ClimateChange.
Read 8 tweets
Feb 1
Stormy Weather.

A thread looking at the first month of 2022 from a very zoomed out perspective. A series of 30 day animations of satellite imagery from @NASA Worldview.

We begin in the South West Indian Ocean which is currently being monstered by a new Cyclone Alley.
@NASA Next stop the South West Pacific which has had several Cyclones, but thankfully none making landfall in NZ. << touch wood >>.
@NASA Staying mostly in the Southern Hemisphere we now look at South America and the extraordinary Amazon Basin which has experienced record flooding and had a remarkable impact this winter on both North and South Africa producing massive atmospheric rivers to the NE and SE.
Read 12 tweets

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