Loc: Orlando, FL
Tropical Storm Bertha Forms South of Cape Verde Islands
Wed Jul 02 2008 07:30 AM
Update - Sunday 07/06, 1130PM ET
Bertha has been intensifying during the day and evening and is nearing hurricane strength, with maximum sustained winds near 65mph, and a minimum central pressure of 994mbs. There is even indications of an eye-wall formulation. This is all likely a result of favorable deep layer shear profiles combined with the fact that she has been moving over gradually warming SSTs. She is currently located near 18.6N/ 48.9W and continues moving west to west-northwest at a brisk 20mph.
This range of motion is being strongly dictated by pervasive Atlantic Basin subtropical ridging and is expected to persist for the next 3 days, keeping Bertha on the west-northwest general heading. After that things get complicated. Modeling solutions range from a rather discerned polar-ward motion ensuing roughly at 72 hours, taking Bertha east of even Bermuda, to bringing Bertha to the outer Bahamas.
Bertha's developmental prospects look good for the next 2 days, after which, some shear may impact her. However, by then she may be a bit stronger of a system and more capable of fending off a harsher environment; provided said environment doesn't become overwhelming, of course. The official call at this hour is 70kts by 24 hours, then hold her own through the end of the 5 day outlook. Position at that time, 30N/66W
Update - Saturday 07/05, 1230PM ET
After passing over marginal SSTs during the last day, 1000mb Bertha has struggled a bit to maintain a 45kt (~50mph) wind. The TC is now entering a region of somewhat warmer water, some intensification is likely to resume. Currently Bertha is carrying a rather well defined and persistent convection plume along her NW semi-circle.
According to the 11am advisory, she was moving more due west over the last 6-12 hours, but the longer term average is really 280 degrees at a rather brisk 21mph. This rapid forward motion may also contribute to some limitation on development. Officially, Bertha is forecast to reach hurricane strength by hour 72.
The forecast philosophy is currently that the subtropical ridge over the breadth of the Atlantic Basin will essentially remain intact enough to persist a general west or west-northwest steering field. As is usually the case, the picture becomes a little less clear nearing day 4 and beyond. Previously, there was modeling indication that a weakness would evolve near the 60W longitudes, and that this would induce a bit of a turn toward the northwest. However, now the models have backed off on that idea and instead lift the weak trough axis back north prior to Bertha's nearing that longitude. Thus, the 3 day modeled average has shifted somewhat south of those earlier indications, even though the very recent trends may have shifted the day 5 position a little north. These types of shifting in model position are not unusual. The best way to correct for them is to assess the general synopsis, then balance those solution against to attain the most plausible scenario. That said, it would seem we will have to monitor this system for a few days.
Update - Thursday 07/03, 1130PM ET
Bertha's intensity has been increased to 40kts (45mph). This is a compromise in Dvorak estimates of tools giving 45 and 35kts. Minimum central pressure is estimated at 1006mb, which is consistent with these wind speeds. She is moving at 280 or essentially west at 14mph. Currently, satellite presentation has improved this evening. It is possible that a nocturnal phase of intensification is underway.
The forecast philosophy is essentially unchanged. Bertha is expected to continue moving on a west-northwest motion for the next 3 days, after which, some shear and a weakness in the steering field ridge may belay further intensification, as well as turn her more toward the NW, respectively. Still, the official intensity call is upwards toward 60kts (near 70mph) by 72 hours, and then holding that intensity through 120.
Update - Thursday 07/03, 1130AM ET
TD2 in the far eastern Atlantic has been upgraded to Tropical Storm Bertha - currently relocated about 190 miles south of the Cape Verde Islands. Maximum sustained winds are at 35 knots and the minimum central pressure is 1006MB. Bertha is moving to the west northwest and that forward motion should continue for the next few days. Only slow intensification is forecast as the cyclone moves over some cooler SSTs (26C) in about 24 to 36 hours. After about 4 days, the future motion of Bertha will hinge on the strength of the Atlantic high pressure ridge.
Invest 93L, beginning to experience some increase in windshear, has not changed much in the past 24 hours and continues to move to the west northwest to northwest at about 10 knots in the eastern Caribbean Sea.
We'll continue to monitor both of these systems over the holiday weekend.
Update - Thursday 07/03, 700AM ET
The area that was tracked as (92L) has now formed into Tropical Depression #2
Update - Wednesday 07/02, 1030PM ET
Newly designated Invest 93L about to enter the eastern Caribbean near Martinique. See the Storm Forum thread for additional details.
A potential early-off Africa storm may be forming over the next few days from what is being tracked as 92L, this system has been showing signs of potential development for the last day or so.
If it does form, it will likely not become any more than a named Tropical Storm, and it likely will not last too long as the conditions ahead of it aren't the greatest. Even so, it appears this will move out to sea before having a chance to affect any land areas. If it does form it will be the first to form this far east in July since Bertha in 1996. The track, however, appears to be much further north than Bertha.
We'll be watching in case any of this changes, but other than being something to watch in the Atlantic, there isn't much to be concerned about here.
Edited by typhoon_tip (Sun Jul 06 2008 11:19 PM)