MIAMI, FLORIDA — One of the main reasons the Atlantic has seen a historically quiet hurricane season this year is ample wind shear plaguing the basin’s Main Development Region, according to a wind shear analysis valid 7 PM CDT on September 14. The map, which plots wind shear in knots across the tropical Atlantic, Gulf of Mexico and Caribbean, shows the vast majority of the Main Development Region filled with red contours, indicating conditions that remain unfavorable for tropical cyclone formation. For now, forecasters say the only realistic chance of a tropical cyclone would come from the Gulf into the Caribbean, along with central and northern portions of the North Atlantic, where wind shear is running much weaker.
Ample Wind Shear Across the Main Development Region Drives Historically Quiet Atlantic Season
The Main Development Region, the stretch of the tropical Atlantic between the coast of Africa and the Caribbean where the majority of the season’s strongest hurricanes typically form, has struggled to produce organized tropical systems this year. Meteorologists point to the sheer coverage of unfavorable wind shear across the region as the primary reason. On today’s map, red contours, representing wind shear values unfavorable for tropical cyclone formation, blanket nearly the entire outlined Main Development Region box, leaving only small pockets of green, favorable shear scattered near the region’s western edge closer to the Caribbean.
Wind Shear Map for 7 PM CDT September 14 Shows Red Contours Blanketing the MDR
The wind shear map, valid 7 PM CDT on September 14, uses a color-coded contour system to plot shear values in knots across the tropical Atlantic basin, stretching from the United States and Mexico in the north down through the Caribbean and toward South America in the south. Green contours mark zones favorable for tropical cyclone formation, yellow contours represent neutral conditions, and red contours flag areas unfavorable for development. Small green pockets appear scattered near the United States coastline and across parts of the eastern Pacific, but within the boxed Main Development Region itself, red dominates the picture almost from edge to edge.
Vertical Tilt From Wind Shear Prevents Tropical Cyclones From Stacking and Intensifying
Tropical cyclones, especially developing ones, need to be vertically stacked, meaning their low-level circulation, mid-level circulation and upper-level outflow all remain aligned on top of one another, in order to notably intensify. Ambient wind shear disrupts that alignment by pushing the upper levels of a storm away from its low-level center, a process meteorologists describe as tilting. Once a developing system tilts too far, thunderstorm activity gets displaced away from the surface low, choking off the feedback loop a tropical cyclone needs to strengthen, which is exactly the mechanism keeping so many disturbances from organizing across the Main Development Region right now.
Strengthening El Nino in the Equatorial Pacific Behind Stronger Mid and Upper Level Winds
Forecasters trace the widespread unfavorable shear back to a strengthening El Nino taking shape in the equatorial Pacific, which tends to enhance mid- and upper-level winds across the tropical Atlantic during hurricane season. That stronger-than-normal wind field is a well-documented pattern during El Nino years, and it is a large part of why this Atlantic hurricane season has run historically quiet compared to recent, more active years. As long as that enhanced shear signal persists across the Main Development Region, forecasters say widespread tropical cyclone development in the open Atlantic will likely remain difficult.
Gulf of Mexico and Caribbean Remain the Best Chance for Tropical Cyclone Formation
Despite the widespread unfavorable shear across the open Atlantic, forecasters note that the Gulf of Mexico and the Caribbean remain the most realistic zones where a tropical cyclone could still form in the near term. Wind shear values across parts of the Gulf and western Caribbean run noticeably weaker than across the Main Development Region, and localized pockets of green, favorable shear are visible on today’s map along portions of the Gulf coastline and near Mexico’s eastern shore. Any disturbance that manages to organize in those areas would face a comparatively more favorable environment than one attempting to develop farther east in the open tropical Atlantic.
Central and Northern Atlantic Also Offer Weaker Shear and a Narrow Formation Window
Forecasters also pointed to central and northern portions of the North Atlantic as a secondary area where wind shear is running much weaker than across the Main Development Region. Green and yellow contours dominate large stretches of the open Atlantic north of about 30 degrees latitude on today’s map, suggesting any system that manages to form there or track northward out of the Caribbean could find a more hospitable environment for at least brief strengthening. Even so, forecasters cautioned that the overall pattern this week remains dominated by unfavorable shear across the bulk of the basin, keeping the historically quiet Atlantic hurricane season on track for now.
