Fig. 1: Morning satellite view across the North Atlantic basin.
Discussion: A tropical wave forms in the outer North Atlantic although development is not expected (Fig. 1). Presence of the convection phase of the Madden Julian oscillation (MJO) across tropical Africa is weakening while shifting east. Consequently, ejection of energetic tropical waves into the outer North Atlantic tropics ease in late July. In the western Caribbean Sea, an upper-level tropospheric trough (TUTT) is persisting. High-level wind identifies the northeast to east wind across the northern Gulf of Mexico to the south of an intense subtropical high-pressure area over Texas (Fig. 2). Weaker northeasterlies stretch toward Central America and loop northeastward across the eastern Caribbean Sea to form the TUTT pattern. TUTT patterns produce upper shear and limit upper-level ventilation that prevent tropical cyclone formation. TUTT can occur, as it is now, during a La Nina climate often linked to cool SSTA in the Nino12 region.
Fig. 2: Axis of high-atmosphere shear identifies a tropical upper tropospheric trough over the western Caribbean Sea.