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Alastair Thompson Profile picture
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Sep 30 • 4 tweets • 3 min read
What is happening in the Carolinas is not just a hurricane. The catastrophic event ahead is probably more due to the Atmospheric River which #HurricaneIAN has directed onshore. The second image here roughly delinates the two.

On the ground however this is one weather event. ImageImage
More on the #HurricaneIAN - Atmospheric River combination, to understand this event in context, this is a very important part of the story.

#ExtremeWeather #ClimateChangeNow.
This thread also looks at this issue. #HurricaneIAN has been embedded in this atmospheric river since it started intensifying explosively.

This combination is I think pretty unusual, and it may lead to unexpected consequences in the Carolinas.
Especially if - as seems plausible - the reason that the storm is so resilient is the adjacent atmospheric river which the Hurricane is also strengthening.

This reminds me of the cause of Pakistan's flooding. Atmospheric rivers are persistent phenomena & this one is colossal.

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More from @althecat

Alastair Thompson Profile picture
Sep 30
I've been trying to figure out how best to visually explain how weird #HurricaneIAN is. This is the perfect illustration.

#HurricaneIAN will split in two, the Western part will head to the Virginias, for a while and then return to the Atlantic coast probably in Maryland.
#HurricaneIAN is a remarkable, and hopefully very unsuual phenomena, two distinct weather systems working together - that have appeared to be a single system for several days.

This, the final act, may be the most extraordinary part of this event. But not the most destructive. ImageImageImageImage
This CMISS animation shows what is happening vert clearly. And this explains a lot about #HurricaneIAN:
- its strength
- its super rapid intensification
- the persistent short range model forecast error
- its ability to remain intact over land
Read 5 tweets
Alastair Thompson Profile picture
Sep 30
This is what I was worried about the interaction between the atmospheric river and #HurricaneIAN.

The Wastern leading edge of the Atmospheric River is now pumping directly into #IAN and it appears to be strengthening over land. The Eyewall is not yet complete. Image
Earlier threads discussing the interaction phenomena.
A closeup satelite view of what is likelu the center of #Hurricane IAN coming ashore at Charleston half an hour ago. Image
Read 7 tweets
Alastair Thompson Profile picture
Sep 30
#HurricaneIAN update.

Four radar images over an hour 1-2pm UST.
#HurricaneIAN's motion is not as expected/forecast.

With sunrise approaching energy from the sun increases visibility of the circulation with the development of rain bands in the South Eastern quadrant.
Spaghetti guidance is tightly clustered on Charleston landfall. After moving inland a very sharp turn W/SW is expected with some models even predicting a return back to the Carolina coast.

Tropical rain all the way to the Great Lakes is possible/likely given the size of Ian.
Intensity guidance is very clear that the storm is expected to weaken - based on landfall today. This will change rapidly if Ian does not weaken or landfall quickly.
Read 15 tweets
Alastair Thompson Profile picture
Sep 30
The NHC's forecasting for #HurricaneIAN remains tricky. Inching closer to the North/South Carolina border. And from satellite data, it looks possible that the center of #HurricaneIan is east of the current line.
The specialist HRRR model, which proved more accurate than the main models in predicting the path across Florida is now in agreement with ECMWF, GFS and NAM-CONUS on the location of landfall, but there is a broad range of intensity from 973-984 mb.
There is also a 6 hour range in arrival time among the four models from 1pm to 7pm. Due to the size of the storm, the impacts of #HurricaneIAN on the Carolinas & beyond are already well and truly underway over night local time.
Read 12 tweets
Alastair Thompson Profile picture
Sep 29
#ExtremeWeather #ClimateChangeNow

#HurricaneIAN Update thread.

Near live 6hr satellite imagery #IAN beginning its exit of Florida over Cape Canaveral and the Kennedy Space Center. And it looks like it started strengthening significantly before it's center crossed the coast.
This wider angle view helps put the storm into wider perspective, in particular its size, and the importance and significance of the massive convective area to the East of Florida from which #TSIan #HurricaneIAN is being fuelled.
The big question now is how will #HurricaneIAN interact with this atmospheric river as it crosses the Atlantic heading towards the Carolinas, specifically, will this extremely complex moist air field strengthen or inhibit intensification.
Read 12 tweets
Alastair Thompson Profile picture
Sep 29
This image shows why #HurricaneIAN was so strong. A Parallel line of supercells in an atmospheric river feeding of the hurricane, and in return providing a much larger area of Convection. And this is also the case with Super Typhoon Noru on the other side of the Pacific.
Interestingly #Noru's burst of intensification on approach to Vietnam coincided with part of the intensification period of #HurricaneIAN
Read 4 tweets

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