Well well. After watching some scenes I decided to make one new calc and remake other one that I deleted for reasons that aren't valid.
Okay, there's people who think this is debunked by the fact that Enel said that Nami is predicting the lightning which is incorrect. Nami has no Observation nor ways to actually predicts where will Enel attack because she isn't mind reading him.
What Nami is doing is predicting the path the lightning will travel once it touches the effects of the Thunder Ball. So she is indeed predicting the path after the lightning is fired and it reaches the area.
But there's the possibility that Nami moved her arm before Enel launchs the attack. But this is incorrect as well. Enel already knows the function of the Clima Tact and he fired the lightning in the very next panel after Nami was surprised by her own achievement and then we see the whole movement.
Sure, she can predict weather and its effects but Enel is a person and has own choice to move if he pleases. Saying that Nami moved her arm and still Enel watching this decided to attack her is incorrect.
With that being said let's get into the calc:
So first thing I need to find is the distance. Fortunately I've got all the necessary data in the same page. But first I'll find some values for Nami that I'm gonna need in this and the next calc.
Half of her arm is 0.2273m (69px).
The orange line will be used in the next calc so dismiss it for now.
Screen is 240px.
Enel is 2.66m (95px) = 21.245029267069459 degrees = 4.7986m.
Nami's arm is 0.2273m (135px) = 29.847226301515327 degrees = 0.28855m.
So the distance is 4.51005m.
Well to find how much did Nami moved her arm I need the total distance of it.
Nami is 1.68m (276px).
Her arm is 0.4626m (76px).
Now we can see a big movement. At first I thought it was nearly 135 degrees but that's the movement of the Thunder Ball while her arm is way back her body and judging by the arm's angle the best value is 180 degrees.
1/2(2*0.4626*pi) = 1.4533007615506384 * 440000 / 4.51005 = 141783.868268041572931564m/s Mach 413
Still consistent with Zoro being faster than Nami at Skypiea.
The second calc
This one is a bit harder to do. 98 chapters later Nami did the first usage of her new Perfect Clima Tact provided by the All Mighty Sogeking and proved her new destructive power. Almost catching herself on the spot.
For comedy purposes Zoro and Sanji were catched by the lightnings but they were totally fine afterwards. You can call this outlier because two of the fastest crewmates didn't dodged but it's a gag rather than a plot point in the arc.Nami is 1.68m (39px).
The distance between she and the cloud is 4.09m (95px).
The distance between her hair and her mouth (using the image from above with Nami being 510px) is 0.1614m (49px).
I'll find the distance calcing the lightning using the marine with a 1.7m (274px).
Screen is 674px.
The lightning's width where Nami was right before the lightning was fired is 0.186m (30px) = 2.4163406505629137 degrees = 4.4097m.
Nami's face (hair to mouth) is 0.1614 (76px) = 6.116488412961731 degrees = 1.5105m.
So the distance Nami jumped is 2.8992m.
2.8992*440000/4.09 = 311894.3765281173594132m/s Mach 909
So slightly above 2x faster than 2 previous arcs. Neat. I find it legit.