Lightnews — Scholar-powered news

Philippe Papin @pppapin.bsky.social · 1d

Its verification time. As of 15z Today Oct 7th, Tropical Storm #Jerry has formed with 40 kt winds.

Pretty clear at this point the #ECMWF has struggled with this genesis case, possibly due to the same amped up gravity wave issues that have plagued the model in the tropics for some time.

1 4 25

Reposted by Philippe Papin

National Hurricane Center Bot @nhcbot.bsky.social · 1d

NHC will initiate advisories on Tropical Storm Jerry (formerly AL95), located over the central tropical Atlantic, at 1100 AM AST (1500 UTC). https://x.com/NHC_Atlantic/status/1975563833306493383

1 3

Reposted by Philippe Papin

National Hurricane Center Bot @nhcbot.bsky.social · 3d

8am EDT Oct 5th -- NHC is monitoring an area of low pressure associated with a tropical wave (#AL95) which now has a high chance (70% 🔴) of formation over the next week. It is forecast to approach the Leeward Islands by late this week. Late... https://x.com/NHC_Atlantic/status/1974805335572693115

4 8

Philippe Papin @pppapin.bsky.social · 3d

I forgot to mention, all the images above are from @pivotalweather.com.

1 6

Philippe Papin @pppapin.bsky.social · 3d

One of these models does not look like the others.

This is a 66h forecast, and while precip patterns look reasonably realistic in the #GFS, #GEM (Canadian), & #ICON, the linear patterns seen on the #ECMWF look out of place in the MDR tropical wave.

We'll see what verification looks like.

1 1 12

Philippe Papin @pppapin.bsky.social · 3d

Translation - One of the weather computer models (Euro) is doing something that is not realistic & that could affect its ability to correctly forecast tropical system development out in the Atlantic Ocean.

Philippe Papin @pppapin.bsky.social · 3d

There is now an MDR tropical wave in the outlook that has a medium chance 🟠 of TCG in the next 7-days.

The 00z Op ECMWF feels like deja vu, gravity waves in wave axis dispersing energy & preventing convective consolidation.

Seems unrealistic, but check back in 5 days to see how it performs. 🌀

1 3 23

Philippe Papin @pppapin.bsky.social · 5d

Yeah using mp4s in general is a little harsh on image quality. Slowing down the animation can help, but it can certainly be lower quality than using .gifs though it also typically means smaller file sizes.

Philippe Papin @pppapin.bsky.social · 5d

I'm not sure how I missed when they made the change, but .gifs now seem to upload & automacially be converted into .mp4's on @bsky.app.

Finally I don't have to convert them myself! I'm probably the last person to find this out, but hurrah! 👍

4 18

Reposted by Philippe Papin

National Weather Service @nws.noaa.gov · 6d

Swells and high surf from Imelda are expected to produce dangerous marine conditions and rip currents along much of the East Coast of the United States during the next several days.

3 29 100

Philippe Papin @pppapin.bsky.social · 7d

This is list that includes tropical storm proximity -- not when only 2 #hurricanes where in close proximity. Still, we are likely moving up the ranking lists of closest interaction on that list too.

1 1

Philippe Papin @pppapin.bsky.social · 8d

And with the 15z advisories -- #Hurricane #Imdelda & #Humberto are just 479 miles apart.

This might be the closest two simultaneous hurricanes have ever been in the Atlantic basin in the satellite era (since ~1975).

Close enough for their outer sfc circulations to interact as well.

Great Circle Distance tool calculator available here -- https://www.nhc.noaa.gov/gccalc.shtml

Weathernerds image of the 06 UTC GFS forecast valid 15 UTC today showing 10 m winds (shaded), direction (barbs), and sea-level pressure (black contours).

2 31 66

Philippe Papin @pppapin.bsky.social · 8d

Yes it's pretty darn unusual to see two #hurricanes in the North Atlantic basin this close. #Imelda & #Humberto.

It has happened recently w/ weaker TCs (e.g., #Philippe & #Rina in 2023), but unsure the last time both systems involved in binary interaction were both ≥65 kt in the NATL.

🌀🔄🌀

6 19

Philippe Papin @pppapin.bsky.social · 8d

Nice thread by Tomer here. Agree it requires nuance when looking at ensemble means to determine how skillful that dataset is for TC track forecasting.

In addition — skill vs spread plots are helpful to see if the ensemble dataset is capturing realistic spread, or if it’s over or under dispersive.

Tomer Burg @burgwx.bsky.social · 8d

Adding my 2 cents to the discussion on Google DeepMind’s performance for Imelda… 🧵

You might see a map like this and be impressed that at no point did it predict landfall in the US. But there is a lot of context lost by simplifying it to just one image.

1 9

Philippe Papin @pppapin.bsky.social · 8d

But maybe diff here b/w #91L vs #Gabrielle, #Humberto, & #Imelda is that instability in late Sep is higher than early Sep & every little bit helps when trying to aggregate convection to get TC genesis.

I still think @btangywx.bsky.social’s argument that mid-lat synoptic variability matters too.

1 1

Philippe Papin @pppapin.bsky.social · 8d

Gotcha… so your argument is an earlier CCKW helped the waves convectively enough to get them over the line to genesis before more neg large scale conditions took back over?

It’s funny how sometimes it works, & other times like #91L it can’t quite get to the point where WISHE can sustain convection.

2 1

Philippe Papin @pppapin.bsky.social · 8d

We are certainly experiencing a later than typical peak, but my confusion was that the sub-seasonal signals suggest conditions are not very favorable *now* in the Atlantic.

Yet we are having our most active period to date. Maybe climo increase in instability helps despite the unfavorable +200 VP'?

Velocity Potential anomalies at 200 mb where +CHI (proxy for downward large scale vertical motion) shows up as brown colors and -CHI (proxy for upward large-scale vertical motion) shows up as green colors.

1 2

Philippe Papin @pppapin.bsky.social · 9d

I sense some good research coming down the pipeline in an attempt to explain the mercurial nature of the 1st vs 2nd halves of September 2025 😃

2

Philippe Papin @pppapin.bsky.social · 9d

Thanks for chiming in! It is still perplexing to see lack of activity in Caribbean/Gulf to date (save Barry). Obviously things can change in Oct/Nov but point 3) resonates since I think seasonal predictions can underestimate how much synoptic variability ultimately drives key TC activity periods.

Philippe Papin @pppapin.bsky.social · 10d

Just posing the question -- I don't have any solid answers & was hoping to generate a larger discussion on why activity has suddenly picked back up without a good large-scale signal for it to do so in the NATL basin.

4 9

Philippe Papin @pppapin.bsky.social · 10d

A provocative question: *Why* is activity in the NATL basin now? NATL is under ⬇️ motion via +VP' at 200 mb.
Maybe near peak annual instability helps? 🤷

@webberweather.bsky.social @ericblake12.bsky.social @drkimwood.bsky.social @tropicaltidbits.bsky.social @btangywx.bsky.social @bmcnoldy.bsky.social

ECMWF analysis of 200-mb Velocity Potential Anomalies globally. Note the +VP anomalies over the North Atlantic and -VP anomalies over the Central and Western Pacific.

Vertical Instability plot using Theta difference in the NATL basin. Note the line for 2025 has been below the avg plot most of the season.

4 2 26

Philippe Papin @pppapin.bsky.social · 10d

Zooming out and looking at the GOES-19 Full Disk View, the western hemisphere is finally acting like September for #TC activity.

While ET #Gabrielle is existing stage right, #Hurricane #Humberto (Cat 4 125 kt) & #TD9 (30 kt) have taken its place.
Also can't forget Hurricane #Narda in the EPAC. 🌀

5 18

Reposted by Philippe Papin

National Weather Service @nws.noaa.gov · 11d

Tropical depression Nine is expected to strengthen and bring tropical storm conditions to portions of the Bahamas through Sunday night. Tropical storm conditions are also possible along portions of the east coast of central Florida beginning Monday, where a Tropical Storm Watch has been issued.

4 28 93

Reposted by Philippe Papin

National Weather Service @nws.noaa.gov · 11d

Advisories on Potential Tropical Cyclone Nine (formerly AL94) will start at 5pm ET, meaning that while it is not a tropical cyclone yet, there is high confidence of it developing and bringing significant wind or storm surge impacts to land within the next 72hrs.

Check hurricanes.gov for the latest.

25 69

Reposted by Philippe Papin

National Hurricane Center Bot @nhcbot.bsky.social · 11d

NHC will initiate advisories on Potential Tropical Cyclone Nine (formerly AL94), located near eastern Cuba, at 500 PM EDT (2100 UTC). https://x.com/NHC_Atlantic/status/1971670145887084834

2 4