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Philippe Papin Profile picture
@pppapin
Jun 21, 2022 • 6 tweets • 4 min read • Read on X
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A June African Easterly Wave (#AEW) is getting ready to emerge off the African coast. While it is quite early in season, there are a couple of factors worth monitoring w/ this system over the next week I'll try to briefly describe --

Image source: @Weathernerds
As this wave propagates westward, a convectively coupled kelvin wave (#CCKW) is propagating eastward & could result in anomalous favorable environmental conditions across the MDR as it passes across over the next week.

Image source: ncics.org/portfolio/moni…
In addition, we had a helpful "sacrificial" lead off system earlier that helped to moisten upstream environment. There has been good literature looking at the importance of the upstream wave environment moisture for ultimate development.

Image source: @TropicalTidbits
Another factor worth mentioning is that sea-surface temperatures (SSTs) in the main development region (#MDR) below 15N are already above 26 C & running a good 1-2 C above average across a large area for late June.

Image source: coralreefwatch.noaa.gov
Okay one plot comparing 200-hPa velocity potential forecast to last year (June 2021).

If you are feeling some #DejaVu, you are not alone. The kelvin wave signal on hovmoller not as strong now, but distinct large-scale similarities w/ 2021.

Source:lab.weathermodels.com/models/ecmwf/e…
Anyway this is a lot of stuff to digest for a signal that is still beyond 5 days out. Only a curiosity at this point in time.

Also typically better to highlight large-scale signals rather than get caught up w/ particular model solutions at this time frame. More later.

-- fin

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More from @pppapin

Philippe Papin Profile picture
Sep 1, 2022
Let's discuss the anomalous NATL high latitude SST warming that occured this Summer + the negative SSTA that shifted equatorward. Remarkable seasonal changes that need an explanation.

1⃣hypothesis: The SSTA pattern was aided by enhanced NATL anticyclonic wave breaking (#AWB).
We've certainly seen our fair share of #AWB events recently. These atmospheric waves break over & over in the NATL, helping define the mean tropical upper-tropospheric trough (#TUTT), individually comprised of potential vorticity streamers (#PVSs) folding under building ridges.🌊
But while upper-level AWB & PVSs are common in the Summer, 2022 has been rather exceptional as seen in the 200mb vector wind anomalies.

Look between 40-45N/10-40W. Thats a 9-10 m/s ENE vector anomaly when the climatological flow is typically 10-15 m/s *westerly*
Read 6 tweets
Philippe Papin Profile picture
Jun 23, 2021
Given the potential historic nature of the upcoming Pacific NW heatwave, though it might be a useful exercise to trace back the antecedent synoptic pattern.

It starts w/ enhanced moisture off Asia enhancing NPAC jet, kicking off persistent ridge building over British Columbia.
The "persistent" amplified ridge over British Columbia is key, b/c it takes multiple rounds of downslope mixing to boost sensible heat fluxes resulting in this heatwave.

Each successive day 850-hPa temps increase over the heat dome until max anomalies are +25C above normal!
Let's put that value in better context

+20-25C 850-hPa anomalies in the middle of Summer are on top of the climo of ~10C in Seattle, WA.

So you are looking at 30-35C 850-hPa temps that can then be dry-adiabatically mixed to the surface given sufficient downsloping.
Read 4 tweets
Philippe Papin Profile picture
Aug 26, 2020
For this elevation (beam height from KLCH is around 16,000ft which is ~550-hPa), these radial velocities seen in the E eyewall of #Laura are incredible. Yes that is an inbound 160-mph velocity... at 550-hPa!

This is a very powerful and deep vertical circulation.
And if you go pixel hunting for the maximum velocity pixel, there are values that are larger than that too. The latest scan for example has a 169-mph pixel!

The @53rdWRS normally samples strong hurricanes at 700-hPa as winds decrease w/ height. This is well above that level!
I’m just gonna continue sharing incredible #Laura velocities in this thread. Now up to 173mph in the NE quad.
Read 5 tweets
Philippe Papin Profile picture
Oct 30, 2019
It's been a hard week for CA w/ major wildfires (#GettyFire, #KincaidFire) affecting the state.

Synoptic weather context is key: Fires were aided by repeated mountain & gap winds via ridge building over the Great Basin. This ridge building enhances the pressure gradient over CA.
The synoptic weather sets the stage, but the mountain interaction enhances the winds further.

Let's illustrate the mesoscale details w/ a cross-section across the coastal CA mountain ranges. Hurricane force (#SantaAna) winds form as cold easterly flow tries to cross the barrier.
The record-breaking cold pool intensity associated w/ a 1045-hPa ridge is one reason why this last mountain wind event for southern California may be the worst.

Inland, 850-hPa temps are at record lows, but adiabatic compression modifies the air to near climo on the coast.
Read 5 tweets
Philippe Papin Profile picture
Sep 2, 2019
Here is the sequel to my steering flow animated explanations. I'm covering 2 periods.

1st period is when #Dorian is expected to stall.

3 Features Cancel out:
1) Ridge over the NATL
2) Ridge over the Midwest
3) Trough that creates a weakness between the two ridges.
So naturally the next question is, what causes the #Dorian to start moving again?

Essentially one ridge becomes stronger (NATL ridge), while the other one weakens (Midwest US), with progressive troughs making sure the weakness stays open. Breakdown below⬇️
So in retrospect, it's not the trough picking up the storm, but rather the transient troughs provide a weakness that then gives #Dorian a path to then be directed around the clockwise circulation of the NATL ridge.
Read 4 tweets
Philippe Papin Profile picture
Aug 30, 2019
Okay so while all attention is on #Dorian, let's do a quick tour of the rest of the NATL tropics currently, because there are some other systems to talk about.

There is a weak llvl circ. n/ Cuba W of Dorian. It should move into the GoM where it has a chance to organize further.
Next up is an African Easterly Wave that just emerged off the coast. The model guidance has been somewhat optimistic on this wave developing over the next 5-7 days, so worth keeping an eye on it. Aside from the Cape Verde islands, no threat to land.
Let's continue. There is yet another wave out in the middle of the NATL basin. Its battling some fairly strong westerly shear currently, but some models suggest it will get into a more favorable environment as it moves off to the northwest. #Bermuda should keep an eye on it.
Read 5 tweets

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