From Jonathan Vigh:
The depression that formed yesterday off the South Carolina coast has become much better organized in the past day and is upgraded to Tropical Storm Gaston, the 7th named storm of August (a tie with 1995 for the most storms to ever form in August). The storm is drifing slowly westward and forecast to make landfall in South Caroline in 24-36 hours. Tropical Storm Warnings are now in effect from the Savannah Rive to Little River Inlet, and watches are in effect for areas on either side of the warning area. A reconnaissance aircraft is currently flying the storm and has found that Gaston is a healthy tropical system with a central pressure of 996 mb. The storm is in an environment favorable for strengthening, so it will likely continue to intensify until landfall. A ridge to its northeast should prevent it from making a quick escape out into the Atlantic. Although the storm probably has at least a one in four chance of making it to hurricane strenth, the primary threat from this system is still the heavy rainfall that it will be producing over the next several days. At 18Z, Gaston was at 31.3N 78.7W with winds estimated at 40 mph, but possibly climbing. Meanwhile, Hurricane Frances has been keeping things interesting over the mid-Atlantic. Frances has strengthened only slightly since yesterday, to 105 kts. Overnight, the storm completed an eyewall cycle, which often happens in intense hurricanes. Although eyewall replacement cycles are not completely understood, basically, outer rainbands form a second outer eyewall which then contracts and chokes off the inner eyewall. This process temporarily halts intensification and can cause a brief weakening. An added side effect is that the storms size can be increased to some extent. Once the inner eye has died, the storm continues strengthening and the new eyewall can shrink in size -- sometimes this cycle occurs multiple times over a storms lifetime. Some more internal fluctuations are expected as Frances continues moving towards the northwest. The vertical shear is still low and the sea surface temperatures are still getting warmer, so Frances is forecast to strengthen into a cat. 4 hurricane. The area of vertical wind shear mentioned yesterday is still present, but seems to be decreasing with time. By the time Frances reaches it tomorrow and Monday, it could be nothing more than a speed bump to the storm. Maybe even more interesting than the intensity is the storm's forecast track. A strong ridge should force the storm to make a turn to the left starting tomorrow. The storm is already slowing down, so this may be an indication that it is getting ready to make the turn. The official forecast still calls for Frances to pass well to the north of Puerto Rico, the Virgin Islands, and the Dominican Republic, but if the ridge is stronger, the turn could occur sooner and the storm could come uncomfortably close to those locations. This is still a distinct possibility (about a 1 in 10 chance), so people in those locations should monitor Frances closely over the next couple days. After that, Frances is forecast to continue west northwest towards the Turks and Caicos islands, which may eventually feel the wrath of Frances starting next Wednesday and Thursday. If the strong ridge continues to hold, the storm could eventually threaten the United States. A potential landfall is nearly a week away, and there are still many factors that could prevent Frances from ever threatening the U.S. Nevertheless, if you live in those locations, it doesn't hurt to review your hurricane plan and resupply your disaster kit. At 15Z, Frances was located at 17.4N 51.9W and moving NW at 8 kts. Maximum sustatained winds were estimated at 105 kts, with a central pressure of 958 mb.
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