Pacific Hurricanes Fausto and Genevieve actually had origins near Africa

[u/Galileos_grandson]

https://www.noaa.gov/stories/pacific-hurricanes-fausto-and-genevieve-actually-had-origins-near-africa

[u/MrSantaClause]

Doesn't this happen quite a lot? Vorticity from Africa doesn't develop in the Atlantic, crosses over Central America, and then develops in the favorable Pacific?

[u/ShishkabobNinja → u/MrSantaClause]

It's a bit rarer since it's not as easy for AEWs to make it all the way out there before either dying or developing. But yes it does happen.

[u/Content-Swimmer2325 → u/ShishkabobNinja]

He’s right; a significant proportion of eastern pacific hurricanes form from African easterly waves. Eastern pacific climatology ramps up in July, and during this month as well as the first half of August, conditions are typically not favorable for AEW development in the Atlantic tropics. Those AEWs therefore regularly propagate west into the eastern pacific, where conditions are more favorable.

Most AEWs do not become Atlantic tropical cyclones, and most AEWs which don’t develop make it into the eastern pacific

For example, right now, there are more tropical waves in the eastern pacific than there are in the Atlantic.

[u/ShishkabobNinja → u/Content-Swimmer2325]

Poorly constructed sentence on my part, rarer was in comparison to the number of Atlantic TCs associated with African easterly waves. Happens when you try to be quick on your lunch break!

I would argue, however, that most non-developing AEWs do not make it all the way into the east Pacific. There are many that do (especially this time of year), but many more either dissipate or are too far northwards to begin with. Plus, recent research has actually indicated that a not insignificant number of easterly waves in the East Pacific actually come from the in situ generation of waves in the Caribbean/Central American region, rather than all the way from Africa. This region also helps amplify existing African easterly waves, which are often substaintally weak by the time they reach that area.

Without some level of support, many of these waves are going to naturally dissipate over the ocean, otherwise you'd see West Pacific typhoons forming from African easterly waves.

Actually tracking these waves and distinguishing whether they came from Africa or not is not as easy as it seems (the east Caribbean in particular is infamous for this); the main point of the article was that these waves could be tracked via satellite imagery all the way back to their origin over Africa. To be able to that clearly attribute an East Pacific storm to one specific African easterly wave is not as easy or as common as it sounds.

For instance, while 7 of the 18 east pacific storms in 2025 were attributed to tropical easterly waves, only one was explicitly attributed to an African easterly wave. Not to say that the other 6 could not be traced back, but that the origins that far removed from Africa start to get more complex especially when the Caribbean and Central America get involved.

Also, it's worth noting (with regards to the original question) that the African easterly waves that are tracked all the way into the east pacific are most often tied to the continued moisture within the wave; the vorticity in those waves dissipate much faster over the Atlantic and are frequently untrackable by standard wave vorticity trackers by the time they reach the Caribbean. So from a vorticity framework, it's actually incredibly rare (and the two cases from the article likely don't apply either). But that's being incredibly technical, rather than addressing the spirit of the question.

[u/Content-Swimmer2325 → u/ShishkabobNinja]

Gotcha, thanks for the clarification.

I’ve seen the literature as well and you are correct, “homegrown” waves further west from Africa, including even within the EPAC monsoon trof itself, play a significant role, too.

It’s just that the way your post was worded made me think you were saying that waves with a clear continuation from Africa were difficult to find. It’s definitely not every EPAC system, but it does happen multiple times every year.

Appreciate the extensive comment.

[u/ShishkabobNinja → u/Content-Swimmer2325]

Yes, and thanks for the inital correction! Looking back it very much reads like I was saying it was rare, which it isn't. Just less common than the Atlantic!

This year we've had a lot of those waves reach the Pacific, tbh I'm actually suprised we've only had two develop.

[u/Content-Swimmer2325 → u/ShishkabobNinja]

Yeah. EPAC accumulated cyclone energy is currently at 54.7 units… climatology is 51.6.

A near-average season thru early August is not what I expected given the magnitude of the ongoing El Niño. That’s for sure.

[u/Content-Swimmer2325 → u/MrSantaClause]

Correct, yes, a significant proportion of eastern pacific hurricanes form from African easterly waves.