Little Change to Julia and Karl in the Atlantic

Like some annoying insect that keeps buzzing around and won’t go away despite repeated attempts to swat it, Tropical Depression Julia continues to spin away a few hundred miles off the coast of South Carolina. Satellite images on Sunday morning showed that Julia continued to struggle with high wind shear, with the low-level center of the storm completely exposed to view and the heaviest thunderstorms several hundred miles from the center. No offshore buoys were reporting sustained winds over 15 mph on Sunday morning.


Figure 1. Latest satellite image of Julia.

Forecast for Julia
Julia is embedded in an atmosphere with very dry air (50% relative humidity at mid-levels of the atmosphere) and wind shear is expected to stay high, 20 - 30 knots, through Sunday evening. These conditions should cause the storm to continue to struggle as it meanders off the coast of South Carolina in an atmosphere with weak steering currents. Wind shear is expected to weaken to the moderate range, 10 - 20 knots on Monday, which may give Julia a window of opportunity to intensify into a weak tropical storm once more. An Air Force hurricane hunter aircraft is on call to investigate Julia on Monday afternoon, if necessary. Wind shear is expected to increase again to the high range, 20 - 30 knots, by Monday night, which would likely stop any further attempts at intensification.


Figure 2. Latest satellite image of Karl.

Tropical Storm Karl continues west with little change
Tropical Storm Karl was headed west at 12 mph in the central tropical Atlantic late Sunday morning, and does not pose a threat to any land areas for at least the next five days. Satellite images on Sunday morning showed much the same picture as the previous three days: Karl had a large circulation and plenty of low-level spiral bands, but the center was nearly completely exposed to view due to moderate wind shear of 15 knots, with the storm’s heavy thunderstorms limited to the northeast side of the center. Karl had marginal conditions for development, with relative humidity at mid-levels of the atmosphere 45 - 50% and sea surface temperatures (SSTs) near 27.5°C (82°F). By Monday, SSTs will increase to 28°C and wind shear is expected to drop to the low range—less than 10 knots. These conditions favor strengthening. However, the atmosphere surrounding Karl will be quite dry through Tuesday, which should slow development.

The track forecast for Karl for the next five days is fairly straightforward, with the steering currents expected to take the storm west, then west-northwest. Karl should clear the northern Lesser Antilles Islands by several hundred miles at the time of its closest approach on Wednesday, and wind up at a point midway between the Bahamas and Bermuda on Friday. At that point, Karl is likely to be a hurricane, and will start generating large swells which will begin impacting the U.S. East Coast and the Bahamas early next week. The big question is—will Karl make landfall on the U.S. East Coast early next week? Hurricane forecasts more than five days in advance are quite unreliable, but residents along the U.S. East Coast can take heart from the fact that a strong trough of low pressure is predicted to pass to the north of Karl early next week. This would result in a recurving path for Karl to the north and then northeast, with the storm missing the U.S. East Coast. This was the prediction from the 12Z Saturday and 00Z Sunday runs of our two top models for predicting hurricane tracks, the GFS and European models. Moreover, more than 90% of the 50 members of the 00Z Sunday run of the European ensemble forecast and all 20 members of the 00Z Sunday GFS ensemble forecast predicted that Karl would miss the U.S. Given these forecasts, it currently appears that Bermuda and the Maritime Provinces of Canada are the only land areas at significant risk from a direct hit from Karl next week. Still, long range forecasts like this are unreliable, and we will have to watch the evolution of the forecast of the upper air pattern in the coming days to see if a landfall along the U.S. East Coast early next week might be in the cards.

96L off the coast of Africa may develop
A large tropical wave with plenty of spin and heavy thunderstorm activity (Invest 96L) was located between Africa and the Cabo Verde Islands on Sunday morning. The tropical wave has favorable conditions for development through Tuesday as it heads west-northwest at 10 - 15 mph through the Cabo Verde Islands. The latest 00Z Sunday runs of our three top models for forecasting tropical cyclone genesis--the GFS, European and UKMET models—all showed development of the system over the next three days. 96L is headed into a region of ocean where very few storms ever threaten any land areas. In their 8 am EDT Sunday Tropical Weather Outlook, NHC kept their 2-day and 5-day development odds at 40% and 70%, respectively.

Jeff Masters