Thread by @althecat

This IR satelllite image [src: @TropicalTidbits] shows #TSKarl is unquestionably now #HurricaneKarl. It also shows it is not moving towards the Mexico coast line as per the current @NHC_Atlantic forecast - but moving NE. And the transformation into this was 3 hours ago.

Here are its first three hours as a hurricane.

And this is the most recent @NHC_Atlantic discussion bulletin for #TSKarl, issued 2 hours ago.

@NHC_Atlantic Which pretty much precisely matches this latest GFS model PWAT forecast which shows pretty much exactly what happened to #HurricaneJulia 2 days ago [see.. quoted tweet].

Is Central America really about to experience groundhog day?

Call me skeptical.

Like #Julia #Karl is endlessly surprising. And now instead of moving West as forecast, after becoming a cyclone/hurricane 3-4 hours ago #Karl has already moved 125kms on a heading just north of east.

#Karl also now has a cyclonic core that is 220kms across.

Karl is now 460 kms from the Mexico coastline and moving further away at around 25-30kmh.

Its now pretty now clear what is going on.

#HurricaneKarl #TSKarl is caught in an atmospheric river generated by #TD99E (in a similar way to how #HurricaneIan was) and headed towards florida - not Mexico.

1. This image shows #Karl & #99E in infrared with two overlays.

a) shear [winds which can slow development - in red/green)
b) + 200-850mb wind directions (in white).

The circular element over Mexico is a high pressure circulation situated between #TD99E and #Karl.

The high pressure system is rotating clockwise unlike the cyclone which is rotating counterclockwise. In the animated image you can see how this works like a pulley water produced in convection is is being exchanged between the two storms, strengthening both of them.

When viewed as an animation in motion it becomes exceedingly obvious where #HurricaneKarl is headed.

Storm #99E is the source point of an atmospheric river which extends over the Gulf of Mexico to Florida.

#KARL is now embedded in an atmospheric river. Due to the high pressure circulation over Mexico (the circular feature in images above) Karl is also recycling water back to #99E on the southern side of the river.

There was a similar situation in West Pacific in July 2021 with 2 hurricanes one in the South China Sea and one north of the Phillipines.

In that instance the storms were locked together, but here #Karl is effectively flowing north east in a river being generated by 99E but supported by moisture flows from the tropical water superhighway, aka the ICTZ, "Inter-Tropical Convergence Zone".