For the most part, the skies over the Caribbean and Atlantic Basins are remarkably clear. This is not typical, given that we are still near the most active part of the hurricane season historically (which was just over a week ago).
There is, however, one notable exception to the current –almost thunderstorm free- quiescence over this sector of the tropical atmosphere. The National Hurricane Center (NHC) is keeping an eye on a collection of clouds, identified as AL98, way out in the Atlantic. If it becomes a named storm, it will be called Ophelia.
This disturbance is roughly 1500 miles east of the Lesser Antilles Islands. Though NHC gives AL98 a 70% chance of becoming a tropical depression in the next 48 hours, it will have to overcome the detrimental effects of dry and windy conditions aloft that lie in its way if it’s going to mature beyond that. Even if the broad low-level rotation it currently possesses tightens up a bit, the organization/unification of the thunderstorm groups that now loosely populate its circulation will take time given the ill-suited surroundings nearby.
The guidance generally takes AL98 on a westward, or west-northwestward, course during the next several days across the tropical Atlantic. At this point, there is little evidence from any of the models that AL98 will become more than a tropical storm.
Part of the reason for AL98’s bearish outlook is tied to the global-scale weather pattern that continues to keep our Atlantic hurricane season relatively quiet.
We are basically in the midst of a multi-week lull that began earlier this month. The large-scale pattern across the much of the tropics really hasn’t budged from its apparent near-term commitment to keep the majority of tropical cyclone formation in the West Pacific.
In recent days, two typhoons (Roke and Sonca) formed in roughly the same region of the westrtn Pacific, attaining the equivalent of Category 3 and Category 2 status, respectively.
Though each of these storms will soon disintegrate in the westerly jet stream as they continue to move poleward away from the tropics, some of the global weather models are predicting additional significant development during the next week in that same part of the world.
Yet the satellite image above centered over the Pacific reveals more than just pretty pictures of Roke and Sonca. It indirectly tells us why it’s so quiet in the Atlantic Basin. Most of the thunderstorm activity in the tropics, as shown by the bright white clouds along the bottom of the image, is located west of the dateline over the northern Indian Ocean, Southeast Asia, and Indonesia. The same governing dynamics that are right now unsettling the tropical atmosphere there are discouraging organized thunderstorm activity in the development regions over the Caribbean, Atlantic, and Eastern Africa.
For the most part, with the noted exception of AL98, this arrangement is keeping a lid on hurricane activity on our side of the world. And there are no obvious signs that things will meaningfully change in the next week.
We may have to wait until October before mechanisms that partly govern the dryness, wind shear, and vertical stability (i.e., resistance to thunderstorm development) over the tropics conspire to increase the likelihood of tropical cyclone genesis in the Caribbean and Atlantic Basins.