Tropical Cyclone Ivan

[Somerset Squall]

The third cyclone currently active in the South Indian Ocean is recently formed 18S, located 770 nautical miles east-southeast of Diego Garcia, and will track generally eastwards throughout the forecast period in response to a near-equatorward rdge to the north. It's quite unusual to have three cyclones active at the same time in one basin, but more unusually they are all moving eastward when generally cyclones in the area head west. It's not rare, just a little unusual.

Anyway, 18S is forecast to strengthen slowly as it heads eastwards (certiainly not expecting any rapid deepening from 18S or 17S like we did with Hondo) under moderate shear and warm sea temps. It's heading away from Madagascar so shouldn't cause too much of a problem at the moment as it heads out to sea. Another one to watch though in this very active period!

Satellite image of 18S (east-northeast of Madagascar with Hondo in the centre and 17S to the right moving towards Australia):

Taken from CIMSS

[Cookie]

[Somerset Squall]

Tropical Cyclone 18S has been upgraded to Tropical Cyclone Ivan. Ivan has significantly intensified and is now at 55kts according to the JTWC. Favourable conditions should ensure than Ivan continues strengthening as it heads generally eastward. A more equatorward turn is predicted beyond 24hrs as a weakness occurs in the equatorial ridge which is currently steering Ivan. Ivan was looking a bit messy earlier but an eye feature is now evident on satellite imagery which is indicative of a strengthening cyclone.

[Cookie]

Its nice when they ain't affecting land. get them intensify more and doesn't cause death or destruction

[Cookie]

forgot to post this earlier!

Storm Alert issued at 8 Feb, 2008 6:00 GMT

Tropical Storm IVAN is forecast to strike land to the following likelihood(s) at the given lead time(s):

Green Alert City(s) and Town(s)

Port Mathurin (19.7 S, 63.4 E)

probability for TS is 45% in about 48 hours

[Somerset Squall]

forgot to post this earlier!

Thanks for the alert Cookie.

Ivan has only intensifed slightly since yesterday with an intensity of 60kts in the latest JTWC advisory. The equatorial ridge previously steering Ivan is no longer affecting the cyclone, and Ivan is now trapped in a very weak steering environment, with little movement forecasted over the next couple of days. Ivan will continue to slowly strengthen as good poleward outflow offsets poor equatorward outflow.

[Somerset Squall]

Ivan strengthened to 65kts this morning but JTWC have the system back down to 60kts and Meteofrance agree Ivan has weakened slightly as they report a pressure of 984mb as opposed to 975mb yesterday. The reason for the slight weakening is due to moderate shear impinging on the system. Ivan looked pretty impressive this morning with a banding eye present on satellite imagery but this is now harder to depict. Ivan's weakening isn't expected to continue however, as shear could relax in the coming few days and poleward outflow is expected to improve. Ivan has been largely quasi-stationary over the past 24 hours but a slow eastward motion is expected to occur due to an southward extension of the equatorial ridge to the north, but Ivan is still expected to move at a snail's pace because a subtropical ridge to the southwest will still be competing to some degree for steering influence. JTWC have Ivan at 85kts by the end of the forecast period. It was originally thought that Ivan will move slowly westwards towards Madagascar but an eastwards motion is resuming which should take Ivan further out to sea. Ivan isn't expected to threaten land yet.

[Cookie]

thanks for the updates.

you can tell its change direction from the wunderground image

[Somerset Squall]

The Meteofrance track for Ivan shows it very well too, it's still unclear just where Ivan is going to go next. This is reflected in the fact that JTWC expect Ivan to very slowly push eastwards and (as you can see below) Meteofrance expect a slightly faster westward motion to resume shortly.

Edited February 10, 2008 by Somerset Squall

[Somerset Squall]

Ivan has re-strengthened in the last 12 hours and is now at 75kts. Convection has increased considerably over the centre after it looked a little messy this morning and a banding eye is also visable. The equatorward ridge is still in control of Ivan at the moment but a subtropical ridge is soon going to be steering Ivan back westwards (Meteofrance and JTWC both now agree on this) at a faster pace. Ivan is forecast to continue strengthening, perhaps quickly, due to warm sea temperatures, mainly low shear and good poleward outflow.

[Cookie]

interesting updates yet again. Im feeling bit useless with out my alerts

[kold weather]

Not much more to say as SS has it pretty well covered, appears a eyewall on the northern side is developing with a clear warm slot appearing in the CDO, classic signs of a eye starting to develop which is about normal for a system that is estimated to be at 75kts.

Also as SS said this system could develop fairly quickly, I wouldn't be all that surprised to see it reach 100kts in the next 24-30hrs but we shall see, much depends on how well that eye develops tonight, will review that idea tomorrow morning I think!

Edited February 10, 2008 by kold weather

[Somerset Squall]

Ivan has intensified further and is now at 85kts, and could well be higher than that by this evening as Ivan is definitely on the up. An eye is clearly identifiable on satellite imagery and a very small eye it is aswell. Banding is really impressive too and Ivan is expected to continue intensifying under favourable conditions. Ivan is just starting to turn westwards too as predicted- which will take Ivan closer to Madagascar. Will definitely need watching if that westward motion becomes a permanent thing.

[Somerset Squall]

Ivan has weakened a lot overnight and is now at 65kts. The eye is very rugged now and most of the deep convection is displaced west of the rugged eye. Ivan has weakened in response to a blast of easterly shear and having moved over lower sea surface temperatures. The weakening could continue for another 24 hours. Beyond that, sea temps are expected to become warmer again and poleward outflow is forecasted to be enhanced by an approaching trough which may allow Ivan to re-srengthen again. This shear and cool sea temps have certainly been a knock back for Ivan but it shouldn't be the end for Ivan as more favourable conditions do lie ahead as it tracks briskly westwards in response to a subtropical ridge to the south.

[Cookie]

thanks for the updates

[Cat 5]

Ivan certainly is keeping a rather strange track...! It is zig-zagging all over the place.

Not sure if this image is working!

[Somerset Squall]

Ivan has weakened further to 55kts and has lost it's eye by the looks of satellite imagery. Continued easterly shear and cooler waters have contributed to the sustained weakening. However, conditions are still expected to improve in a couple days time with shear easing and sea temps rising along the westerly track.

[Cookie]

its the drunk man on a Saturday night again!

Edited February 12, 2008 by cookie

[Somerset Squall]

Ivan's a real mess right now (rather like the drunk man on a saturday night ) and it's intensity has been decreased to 40kts as shear and low sea surface temperatures persist. However, shear is still expected to ease and sea temps warm up, and this, coupled with increasing poleward outflow ahead of a trough should induce strengthening, particularly after 36 hrs.

[Somerset Squall]

Ivan has intensified back up to 55kts (Ivan certainly has been an up and down storm!), and a banding eye is now visable in latest satellite imagery. Ivan is expected to continue intensifying as an anticyclone lessens the shear and poleward outflow increases. Ivan is expected to continue to head westwards on the northern periphery of a subtropical steering ridge but a poleward turn is expected later in the forecast period, though it's uncertian exactly when this will occur.

[kold weather]

I have to admit I weren't entirely sure that Ivan was going to restrengthen so a good call by the forecasters, its fair to say that this system is a battler. Anyway shear has eased off nicely and once again like 36hrs ago Ivan finds itself in increasing heat content and importantly weaker mid-level shear which was really ruining the systems structure. Microwave imagery showing eyewall reforming as well as a eye developing with good inflow on the western side and looks like the system could develop farly quickly again for a seocnd time, could well be a threat to E.madagascar, much depends on how long it rides westwards along the high pressure.

Whilst I did say before that I though Ivan would reach 100kts (10 min sustained) which busted, I wouldn't be all that surprised if that actually happens this time however I've not looked at the shear tendancies enough to really make that call...lets just say there is a chance of such a thing happening, I won't put my head on the block just yet I've got to work my way back into the tropics again so I'm ready for the atlantic season hehe!

Edited February 13, 2008 by kold weather

[Cookie]

thanks for the updates

[Somerset Squall]

Thanks for your thoughts KW, I'm sure there will be plenty more storms to put you back in the frame of mind for the Atlantic season . It'll be interesting to see how strong Ivan gets this time and indeed if it will impact Madagascar later on.

It's also interesting to observe that Ivan is very near the same area in which it formed 6 days ago!! Certainly shows what a slow, erratic mover Ivan has been so far.

Edited February 14, 2008 by Somerset Squall

[Cookie]

if thats true why am I only just getting alerts?

[Somerset Squall]

if thats true why am I only just getting alerts?

Probably because Madagascar may only be affected in several days time, Ivan still has a long way west to go before it makes any possible landfall (still highly uncertain at the moment). Ivan's certainly going to be long lived.

Unisys tracking shows the loop very well:

Edited February 14, 2008 by Somerset Squall