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Posted: Tue Sep 25, 2007 1:41 am
Tuesday Early AM Update
Tropical Depression 12 officially formed late Monday night. It was probably in existance for the previous 12 hours. It will very likely be named Tropical Storm Karen during the day on Tuesday. Deep convection surrounds the low center which Quickscat estimates near 10N / 37W or about 1630 miles east of the Windwards.
Once Karen forms, it is quite likely that a trough will steer the system away from the Lesser Antillies toward the open Atlantic in four or five days. This track still needs to be watched closely to make sure the strength of the trough was forecasted well.
Posted: Tue Sep 25, 2007 8:56 am
Tuesday Late AM Update
Karen was upgraded to tropical storm at the 5am advisory. The center is near 10.5 N / 38W or about 1560 miles east of the Windwards. It is strengthening at this time, but may start fighting wind shear in the next day or two. The forecast still calls for a turn to the open Atlantic, but models may not be reliable on the strength of the trough several days out. Keep an eye on this one in the Leewards until the turn is confirmed.
Posted: Tue Sep 25, 2007 5:50 pm
Tuesday Evening Update
Karen is near 10.5N / 40W or a little over 1400 miles east of the Lesser Antilles. It appears that NHC has estimated the position a little far north at 11.1 N. Either way, wind shear is not posing any problem at the present time. It will continue to move just north of due west before encountering the trough in a couple of days. This trough should start to yank it northward turning it before it gets to the islands. NHC says it will not reach hurricane strength before it moves into the shearing winds. Right now that is a tough call and we think that it is possible to become a minimal hurricane before encountering the trough.
Posted: Wed Sep 26, 2007 1:46 am
Wednesday Early AM Update
Karen is near 10.5N / 40.7W or about 1375 miles west of the Windward Islands as of 2:45am. We're not sure why NHC continues to give a latitude of 11.1N still. the I.R. and Quickscat indicates that the low is about 1/2 degree farther south.
After a lull, Karen is now strengthening. Convection is starting to build near the center of circulation and no appreciable shear is evident. We still believe that Karen could make hurricane status before the trough begins to shear and turn the system.
The latest forecast track still turns Karen northwest before reaching the Lesser Antilles.
Posted: Wed Sep 26, 2007 9:51 am
Wednesday Late AM Update
NHC also has seen the recent strengthening trend and has moved Karen up to 50 mph. Since last night, it appears that Karen has felt the affects of the trough to the west. The western side of the system has far less convection. The overall satellite appearance is excellent though in the sense that it is now rapidly organizing and it taking the shape of a much better structured tropical cyclone. The new advisory will be in soon and we expect additional strengthening. The effect of the trough has significantly yanked the low more northwest with the center at least up to 12.5N now. We will update again shortly.
Posted: Wed Sep 26, 2007 10:13 am
Wednesday Late AM Update - part 2
NHC agrees with the rapid strengthening. New advisory has Karen at 70 mph. It looks like our earlier prediction of Karen possibly reaching hurricane strength before the shearing will come true soon.
Posted: Wed Sep 26, 2007 6:43 pm
Wednesday Evening Update
Karen is now rapidly moving NW. NHC recently said that they tossed out the GFS solution because of it moving too rapidly at first. Well, it looks like the GFS is a winner, because the motion certainly has picked up!
We put the latest position near 13.5N / 44W with aid of the I.R. satellite and the Quickscat. The re intensification has started again and it has probably just crossed the hurricane threshold as cloud tops have cooled rapidly over the center. NHC has it becoming a hurricane now by tomorrow morning.
The track should keep Karen safely away from the Lesser Antilles.
Posted: Thu Sep 27, 2007 1:41 am
Thursday Morning Update
NHC acknowledged that Karen was probably a hurricane briefly before a research aircraft arrived. They kept the strength at 70 mph on the 11pm advisory since the convection had calmed down. The last forecast keeps Karen under hurricane strength.
We disagree with this assessment. Over the past several hours deep convection has developed over the center and what looks like an eye wall is appearing in the satellite imagery. We feel confident that Karen is at least 75 if not 80 mph at this point. NHC should upgrade Karen at the 5 am advisory to hurricane strength.
The models continue to take Karen northwestward over the next five days away from the Lesser Antillies. We will need to watch the extended range because a few of the models want to turn Karen west after that. So, we will need to see if the trough is strong enough to take it out or not.
Posted: Thu Sep 27, 2007 9:57 am
Thursday Late Morning Update
A remarkable transformation has occurred since the middle of last night. Wind shear has ripped the convection away from the center of circulation almost like Karen hitting a brick wall. The deep convection is on the eastern side of the circulation. Certainly Karen's brief time as a probable hurricane was short lived. With the center is now totally exposed, this will allow for a further west motion. The forecasts call for Karen to still recurve to the northeast of the Lesser Antilles, but we will watch this with caution, since the convection has been ripped away and it make take more of a westerly course than previously thought,
Posted: Thu Sep 27, 2007 1:49 pm
Thursday Afternoon Update
Karen has been sheared like a sheep. As we mentioned earlier an incredible turn around from unofficially hurricane strength in the middle of last night to the center completely exposed. The only convection on the eastern side remains. Karen will no doubt move farther west than expected unless convection makes a come back. Don't let your guard down in the Leewards yet.
Posted: Thu Sep 27, 2007 7:19 pm
Thursday Evening Update
Karen continues to be a very interesting feature. As fast as the shear began late last night, it now has dropped. Deep convection has quickly returned over the center of circulation, but not quite over to the west side. No doubt it has strengthened from the 60 mph at the 5 pm advisory. It probably isn't quite to hurricane strength though. This strengthening isn't all bad. The upper air winds will gain hold again which should allow for the turn before the islands.
Posted: Fri Sep 28, 2007 2:01 am
Friday Late AM Update
The latest satellite imagery is in and it shows Karen clearly moving north. NHC in the 5 am advisory had it moving west-northwest. It is possible that since NHC did not have the visible imagery in the advisory that they went with "extrapolated flow" and thought for sure it would continue on its track from last night. We will be curious to see what happens on the next advisory. Our next update will be in the early afternoon.
Posted: Fri Sep 28, 2007 12:11 pm
Friday Afternoon Update
NHC continues to baffle us.
The 11am advisory says that Karen is weakening and still moving west-northwest. We are really curious if the visible satellite imagery is being studied at all. Karen is clearly moving due north. It is moving right along a line of longitude when the grid is overlaid the satellite imagery. The low level center is stripped of convection and can not be mistaken. :?
Over the past couple of hours deep convection is exploding on the east side again. So, as in the past, it is pulsing. Waves of stronger winds aloft strip the convection then weaken and the convection comes back.
Still keep an eye on this one in the Leewards and the states. It is likely to be around for awhile.
Posted: Fri Sep 28, 2007 5:51 pm
Friday Evening Update
With the last visible satellite images of the day we see that Karen is now moving more northwest which now actually agrees with the NHC assessment.
In their latest dicussion, they mentioned the "unpredicted" northward motion. We're not sure what this means since this northward motion was observed for the last almost 12 hours. :?
As of 5 pm NHC says that Karen is barely a tropical storm at 40 mph. We think to be more generous. Heavy convection is still on the eastside and there probably are winds of 50 mph or more.
NHC takes Karen down below tropical storm status and move it generally northwest for several days. The models are a bit confounded in the long term as to what direction Karen will go. Some take it into the central Atlantic with the front, others leave it farther south. Either way, in the short term forecast we think Karen will hold onto minimal tropical storm strength or drop to tropical depression status since the trough to the west is dominating.
Posted: Sat Sep 29, 2007 10:09 am
Saturday Morning Update
Karen is a depression and continues to be ripped apart by "the shear of death". The strong upper air westerlies has continued to weaken Karen. Some deep convection remains well on the eastside of the circulation. The surface low is also weakening and becoming elongated.
The track continues to take it northwest over the next several days north of the islands. Keep an eye on it, but right now, it will not pose any threat for a while and possible never will if the shear continues to work on it.