The GEFS and Euro AIFS ensembles trying to give me some hope for snow in early December. Surely, this must be a trap.

The low-level westerly wind burst in the pacific is what’s really driving the MJO into the Western Hemisphere (phase 8) in Dec (left) That to me is a very telling of how hard the atmosphere is pushing the ocean away from La Niña & possibly towards an El Niño state this coming spring or summer

The warmest water on the entire planet is sitting ~160E in the Equatorial Pacific & a prolonged Westerly Wind Burst event is about to occur here This will trigger a downwelling oceanic kelvin wave that should destroy La Niña ~3 months from now & begin moving the ocean towards El Niño conditions

We might be in a La Niña at the moment, but the tropical troposphere already looks very El Niño-like with a huge build-up of deep-layer westerly wind anomalies In the grand scheme of things, El Nino is likely knocking on the door 🚪

For all my S2S junkies out there, here’s another invaluable tool to add to your arsenal: An annual archive of polar cap geopotential height anomalies going back to 1940 using ERA-5 & a 30-year sliding climatology 👀 hebweather.net/prod/gph_arc...

Cool study came out earlier this yr looking at the dynamical origins of the extreme 2023 Heatwave in the Desert SW They concluded that the warm Tropical Atlantic was the primary culprit The partial regression analysis (left) & AGCM forcing (right) are pretty telling www.nature.com/articles/s41...

I still can’t get over how similar this year’s zonal wind anomalies in the tropics are to 1981

Quietly while La Niña persists, the tropical upper troposphere is becoming very El Niño-like A large build-up of westerly momentum (+U) in the tropics is being supplanted by a West Pac MJO orbit & repeated bouts of positive E Asia Mtn Torque (+EAMT) fluxing/squeezing +U equatorward

The global tropics zonal wind anomalies this year are evolving very similarly to late 1981, which of course preceded a “Super” El Niño event in 1982 Note how this yr & 1981 have a big & slow westerly wind burst over the Indian Ocean & Maritime Continent in Oct-Nov that moved into the Pacific in Dec

As you might expect from the very strong -IOD event strengthening La Nina’s footprint globally, this October’s observed pattern has deviated very little from the last 30 years worth of La Ninas over N America

The latest Euro weekly forecast thru mid-December is almost exactly what you’d expect for typical a La Niña December over the last 30 years: A faster-than-usual start to winter over the East-Central US with plenty of high-latitude blocking

La Niña is living on borrowed time. The extreme -IOD we're currently seeing (right) is about to collapse because the warm water in the Equatorial Indian Ocean will get flushed into the tropical West Pac at depth over the next month in this MJO event's westerly wind burst (left)

This winter seems to be intent on following the cool ENSO/East QBO/solar max paradigm of early winter -AO/-NAO I replicated Gray et al (2004)'s analysis except used SLPa from 20CR & isolated -ENSO (left), which is close to the latest Euro weekly forecast (right) journals.ametsoc.org/view/journal...

Worth mentioning, this year has the 2 main precursors to a -EPO/+TNH ("polar vortex" pattern) dominated winter in place atm as identified by Zhong & Wu (2023). Namely, a warmer-than-normal Maritime Continent & West Pac as well as a Eurasian Snow Cover Dipole. journals.ametsoc.org/view/journal...

Much like last year, the very warm Tropical Indo-Pacific Warm Pool (IPWP) is going to play a major role in this coming winter. Compare the current global mean SSTa (left) to the Oct-Nov Warm Pool SST [20S-20N, 90-150E] difference for east QBO/cool ENSO winters only (right)

Multi-panel view of the last few days of Hurricane Melissa: ↖️ GOES-19 infrared brightness temp ↗️ GOES-19 visible satellite ↙️ Hurricane hunter planes & flight paths ↘️ Recon-derived flight level wind swath ⬇️ Estimated minimum pressure from recon dropsondes

One characteristic of Hurricane #Melissa that'll always stick w/ me is its lack of "classic" eyewall replacement cycles. I honestly can't help but think the environmental +SRH was a factor for that, as this modeling study from earlier this yr showed: journals.ametsoc.org/view/journal...

Wow. This is easily the most ridiculous dropsonde I’ve ever seen. 188 knot mean winds in the low-levels with gusts over 250 mph Absolutely scary and historic hurricane headed into SW Jamaica this morning

Let's play a game of find where local sunset occurred over Hurricane #Melissa

After the conclusion of this hurricane season, we need to have a real, serious discussion about the utility and validity of sticking with standard reduction techniques for estimating sustained surface winds from flight level in really intense hurricanes.

This latest dropsonde in Hurricane Melissa is mind boggling. 185 knot mean winds in the lowest 150m!!! This reduces to about 155 knots at the surface, a good bit higher than the current NHC estimate of 145 kt and actually very much in line with satellite consensus (SATCON)

Even with all of the structural, intensity, and SST/OHC changes underneath Hurricane #Melissa the last few days, the diurnal cycle still remains undefeated and inevitable

Holy mackerel, what a dropsonde…. This explicitly supports Melissa being a 145-150 knot hurricane 😳

Melissa strengthened into a cat 5 hurricane overnight, w/ winds of ~160 mph & central pressure of 913mb. Even more strengthening is likely later today, which may put this storm in pretty rarified air historically for Atlantic hurricanes. Awful situation unfolding for much of Jamaica

This is probably the most tone deaf take I've seen from a professional on wxtwitter and social media more broadly speaking during a natural disaster. Not a good look.

Man tropical weenies are getting trolled hard tonight

A renewed bout of intensification is likely ongoing with Melissa as the central dense overcast continues to appreciably cool after sunset. Also noticing the development of an enveloped eyewall lightning (EEL) signature here, often a signature of a high end category 4 or 5 hurricane

Imho, the structural & intensity changes we‘re currently seeing w/ #Melissa are largely tied to the diurnal cycle. Namely, a radially outward propagating gravity wave causes cloud tops to cool at large radii by the early morning, while the inner core warms. This is precisely what’s happening atm

Tail Doppler Radar (TDR) data from the current recon mission into Melissa shows that the vortex is vertically stacked up to 15 km w/ the upshear/NW quad being the strongest. This is about as favorable of a vortex structure as you’ll see for rapid intensification Plots from @cyclonicwx.bsky.social

While Hurricane Melissa's environment at first glance doesn't seem too favorable for rapid intensification w/ 20-25+ knots of mid-level shear, there's lots of little subtleties here that argue otherwise. Namely: the northerly wind shear vector, deep-layer +SRH, weak inertial stability, & high SSTs.

If #Melissa finds its way south-southwest of Jamaica in several days, this environment has the highest ceiling for any Atlantic tropical cyclone I can remember. Big, strong, slow-moving hurricanes like what #Melissa may become are when things like Oceanic Heat Content will start to matter a lot.

#Melissa has struggled w/ wind shear today & the vortex remains very tilted It's common for weak TCs like #Melissa to struggle in the Central Caribbean, an area of the Atlantic known as the Caribbean "Graveyard" Here's a mini-🧵 on what the Caribbean "Graveyard" is & why it matters here:

Lol. We better hope that #Melissa doesn't take the western end of the track envelope over the Western Caribbean next week because uhhh yea 👀

Invest #98L is steadily getting better organized over the SE Caribbean today. Fast low-level trade winds in the Caribbean "Graveyard" are the biggest impediment to development in the near-term. Once #98L gets to ~75W where the trade winds are slower, much more rapid development is likely

It's still early, but the subsurface Equatorial Pacific temp anomalies atm look similar to yrs where La Nina transitioned to El Niño in the following spring/summer The thermocline isn't exceptionally shoaled in the E Pac & the Indo-Pacific Warm Pool has snuck across the dateline at depth

I still can’t get over how closely last winter’s mean pattern matched the warm Western Equatorial Pacific (WEP) regression pattern in observations & climate model simulations in Kao et al (2024) agupubs.onlinelibrary.wiley.com/doi/full/10....

Imho, the real wildcard for seasonal forecasts the next several months (esp late winter & spring) will be: how much does the Indo-Pacific Warm Pool expand eastward? An initially warm Indo-Pacific Warm Pool, east qbo, & pacific meridional mode all favor some +ENSO advancement next spring

Much like last winter, another +TNH dominated winter is likely staring us in the face thanks to La Niña & perhaps more importantly, a rather warm Indo-Pacific Warm Pool. It will likely have at least a slightly different flavor this time around though…

#Jerry alive yet again

Really intriguing study on the impact of inter-basin SST warming on teleconnection patterns during the strong El Nino winter in 2023-24 www.nature.com/articles/s43...

Invest #96L in the far NE Atlantic is likely becoming a subtropical cyclone, as moderately deep convection persists over the low-level center

The first significant positive East Asia Mtn Torque event of the season will occur late next week into the following week. This will yield a strong, extended Pacific Jet Stream (+EPO) in late Oct & encourage MJO/CCKW propagation across the Maritime Continent & West Pacific late Oct-early Nov.

I wonder where the Rossby Wave Train is

#99L is certainly a tropical cyclone if I've ever seen one. Prominent curved banding under the hood w/ persistent, continuous, & highly concentrated vortical bursting over the same part of the wave axis are dead giveaways that a strong, closed, & coherent low-level vortex exists

Beyond #Erin, this tropical wave leaving the coast of Africa will be the next system to watch in the Atlantic. The overall environment looks quite favorable for development as this reaches the Central Atlantic later this week, esp. as a Kelvin Wave (blue contours, right) passes overhead

#Erin is just a downright incredible hurricane. I cannot remember the last time I tracked an Atlantic hurricane with a pinhole eye this small & stable/persistent since at least Wilma (2005). This evening's recon flight into #Erin ought to be very interesting to say the least

A Convectively Coupled Kelvin Wave that developed within the Subtropical Jet Stream over Northern Australia will likely pass over the Atlantic ~Aug 20 This will favor more opportunities for tropical development late month as a series of strong African Easterly Waves immediately follow behind #97L

There will likely be at least more opportunities for tropical development immediately behind #97L as a Kelvin, Rossby, and MJO wave simultaneously pass over Africa this week. Also, upstream wave dispersion from #97L will only help further amplify the AEW train over Africa

Flooding from Invest #97L caused 6 deaths in the Cabo Verde Islands. Probably would have been a good idea to use the “PTC” designation here. expressodasilhas.cv/pais/2025/08...

I suspect the low-level/convergent portion of a Kelvin Wave is already hitting invest #97L out over the Cabo Verde Islands, giving it an additional instability boost against marginal SSTs Last night's ECMWF 700mb fcst for 0z this evening depicts this quite well misva.aeris-data.fr/products/syn...