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Tropical Twins

Posted by Andy Johnson under Daily updates

The tropics continue to evolve into the active phase we have been expecting. Hurricane Danielle, which had briefly dropped back to tropical storm strength on Tuesday, has been solidly exhibiting hurricane characteristics Wednesday.  Conditions are generally favorable for slow intensification over the next few days. The central core of intense convection has increased in aerial coverage since yesterday. Banding has been most prominent on the east side of the hurricane which is consistent with the fact that Danielle has been experience some southwesterly shear.  Danielle has also broken away from the grip of the large Saharan Air Layer (SAL) which was partly responsible for her decrease in intensity on Tuesday. Most guidance continues to show recurvature. There is no threat for Florida. In the long term there is some uncertainty about whether the recurvature will complete before coming close to the Canadian Maritimes or possibly offshore of the northeast U.S. Residents of Bermuda should also monitor the progress of Danielle and Earl, as well. Tropical Depression #7  continued to show intensification with good outflow in the eastern semi-circle became Tropical Storm Earl at 5PM Wednesday. The enhanced satellite image below shows the high bright white cirrus clouds spiraling clockwise on the north and east sides of the system.

A new convective cluster is just now moving off of Africa. As it has been exiting the continent today, the areal extent of heavy convection has decreased leaving an unorganized, unsymettrical area of clouds and showers. Nontheless, there is a chance that this wave will slowly develop into a depression or tropical storm in the 3 to 5 day time frame. Note that each successive disturbance is exiting Africa at a further south latitude. The further south a wave exits Africa ,the more likely that is has a chance of making all the was across the Atlantic without being picked up and recurved by a mid-latitude trough.

The frontal wave in the Central Gulf of Mexico continues to produce a large area of unorganized but widespread convection in the Gulf. Steering currents will push this system slowly westward or southwestward away from Florida over the next few days. There is only a slight chance of this system developing into a depression before reaching the Texas coast. 

Convection persists in the southwestern Caribbean but there is no circulation evident.

The close-up enhanced GOES IR image below centered over Danielle shows a moderate sized area of deep convection. Two major feeder bands are located on the east side of the hurricane away from the influence of southwesterly shear.

The MODIS AQUA polar obiting satellite image below shows the large round central dense overcast (CDO) is just slightly off center to the right from the low level circulation which can be seen in the lower level clouds. This is another reason that only slow intensification is forecast in the near term.

The AQUA MODIS picture below is Earl. It does not have the circular appearance like Danielle (above) since it is an immature system at this point in time. There are still lots of heavy convective clusters, though.

The Saharan Air Layer (SAL) graphic below shows that Danielle has freed herself from the SAL dusty grip. Earl, however, is headed into a dry dusty area to the west. Eventually the new wave moving off of Africa,which will likely become T.D. #8, may encounter some dusty air in about 2 days. The dusty air inhibits tropical cyclone development and intensification.

Another technique to view the amount of moisture in the air is the water vapor satellite imagery. There is still a persistant layer of dry air west of Danielle with another slot west of Earl.  The moist circulation of Danielle seems to be eroding the dry patch of air further west, though.

As alway, use caution in looking at long range models since there is a great degree of uncertainty and wide errors. General trends can sometimes be gleaned from then, though.  The 12Z run of the GFS model show that by next Tuesday, Danielle will likely still be a hurricane and will be located east of New England. Earl will be located north of the Leeward Islands by that time. The new wave just moving off of Africa today, could become Fiona located east of the Leeward Island. Note that with each succesive storm, the track is a bit more south and west.  

Hurricane Frank fortunately missed a directly hit on the Mexican Riviera but could eventually bring some moisture to Baja California by Monday or Tuesday next week.