My overall take on Hurricane #Helene is:

While the forecasts from the NHC, WPC, & local NWS WFOs certainly couldn't have been much better overall, how that forecast was presented, communicated, and then acted upon by both the public & decision-makers was far from sufficient to put it lightly.

This on top of the other socioeconomic issues (w/ the hardest hit areas also being generally isolated & poor) has greatly exacerbated the disaster that's ongoing in/around western NC... (1/n) It's easy to point fingers & blame local, state, federal governments, etc. for an apparent lack of or a slow response, but it's a lot harder to look in the mirror & ask yourself what WE can do as meteorologists to better to communicate this information & get these folks to act more accordingly next time... (2/n)

An often overlooked element in seasonal hurricane forecasts is how the tropical mid-upper troposphere will respond to an increasingly warmer background climate. The influence of climate change in this hurricane season's abnormally quiet start thus far through late August (relative to expectations) is very likely non-negligible in this case.

While sea surface temperatures have been record warm lately, the upper troposphere has been warming at an even faster rate (!), as shown in the quoted tweet below.

This long-term, increasingly stable trend in the tropical troposphere is also consistent w/ what's expected from climate change.

The increasing stabilization of the tropical troposphere is due to moist adiabatic adjustment in the tropics. Moist adiabatic adjustment causes the deep-layer temperature profile to stabilize in the tropics, w/ the upper troposphere warming faster than the lower-mid troposphere. The combination of more marginal lapse rates & greater saturation vapor pressure deficits also makes dry/stable air intrusions more effective at inhibiting tropical convection in a warmer mean climate (see attached figure).

Simply put, there's a lot more to seasonal hurricane forecasting than record high SST anomalies.

For more, see:







journals.ametsoc.org/view/journals/…
agupubs.onlinelibrary.wiley.com/doi/full/10.10…
nature.com/articles/s4146…
nature.com/articles/ngeo1… There's been a lot of discussion (myself included) about how far north this year's easterly waves have been lately & how this may be inhibiting TC development.

In that context, it's hard not to notice how this summer has been the hottest one on record for much of the Sahara & how it's hydrostatically coupled w/ record low SLP anomalies in NE Africa.

These lower SLP anomalies are indicative of a stronger Saharan Heat Low, which is helping to draw the low-level ITCZ further north, esp over east-central Africa. The end result is what's likely going to be the wettest summer on record for much of northern Chad, southern Libya, & southern Egypt via ERA-5.

Hurricane #Ian is starting to undergo extratropical transition tonight on its way to the Carolinas. Notice the big dry slot sneaking in from the SW and frontal boundary extending from #Ian's south into the Bahamas... Fwiw, one of the simplest methods I use to discern b/t tropical & extratropical cyclones is to locate the subtropical jet & assume everything poleward/north of that is extratropical, while to the south = tropical. #Ian is in the middle rn => "hybrid" warm core/subtropical cyclone

In the coming days, you'll see many Velocity Potential & Madden Julian Oscillation (MJO) plots on #wxtwitter.

Here, I show what they often entail for Atlantic tropical cyclone (TC) activity.

Notice the Atlantic is most active (🔴) when the MJO (🟢) reaches Indonesia (phase 4) Upper left: (5x5°) daily IBTrACS TC track density anomaly vs 40-yr sliding base pd w/ 2 wk-centered climo (+/-7 days)

Lower left: (1x1°) ERA-5 daily 200mb Velocity Potential Anomalies (VP200a) (1979-2020 climo)

Right: MJO phase diagram w/ shading corresponding to spatial VP200a