Cyclone season! As I write these lines, tropical storm Calvinia is battering our small island. You know, the usual: heavy rain and wind gusts. But the dogs and I are sheltered inside my little house, and as long as things don’t get much worse, we’ll be fine. I have made sure I didn’t need to shop for a few days, and have filled up the reserve of diesel fuel for the generator. Right now, I don’t even have all the windows fully closed yet. Even though you must never close all windows and doors in a cyclone anyway, as otherwise the pressure inside, higher compared to the outside with the fast moving winds, can blow out a window. Bernoulli’s law? Something like that. You know, the one that makes airplanes fly.

But when I look out onto the sea, I see white crowns on each and every wave. As diver, I have learnt decades ago that when you see these crowns in the open sea, ie. not close to the shore, it’s bad out there. Don’t-even-think-of-going-out bad. Probably no diving tomorrow.

For a week or so it was clear that the storm would form, and also pass close to Mauritius. is the best source, which we routinely consult on a daily basis during the cyclone season. It uses model based data by ECMWF to predict wind, weather, and sea conditions.

Here’s the current information:

From the small difference between the pressure values on the centre and the outside, and hence how far away from each the the isobar lines are, you see that the storm is not very strong. If the centre pressure were at, say, 950 mbar or even less, things would be different. Potentially violent.

The local government weather services only issue cyclone warnings some two days ahead, that is, when the rough conditions are imminent. I guess their rationale is to avoid false warnings, but I don’t know for sure. I always think they are a bit late in order to give people sufficient time for preparation.

And there’s the US Navy’s website, the Joint Typhoon Warning Centre, which is also useful, both for early warnings and detailed information.

There you find reports such as this one, which covers Calvinia. From the format alone you can tell that it’s not directed to a general public.1

So fingers crossed, for now, we’re just waiting this one out. I mean, what else can be done, right? The doggies seem content at least:

Yes, I know it’s a pretty bad picture. But if I try to lower my perspective, they come running to me… they are friendly dogs.

I somewhat hope the bad weather will hold until tomorrow New Year’s eve – potentially way fewer fireworks scaring my doggies…

Update, 12:45

Calvinia has been rather stationary in the past few hours, and has now started to turn its direction to south-west and to intensify. The cyclone hugs the island. Check out the decrease of the pressure value in the centre, as well as the smaller distance between the isobars. The government cyclone warning has been upgraded to class III.

And the model-based prediction looks even worse (tomorrow, 10:00):

The higher pressure gradient results in higher wind speeds, reflected as red-ish and purple colour on the model map.

Still not a disaster, but serious. This will take longer than expected.

  1. I have formatted this as PDF, on JTWC’s website it appears as plain text in your browser! ↩︎