When vertical wind shear is weak or favourable (below 15 knots), a tropical system can strengthen in intensity and size. When vertical wind shear is strong or unfavourable (above 25 knots), a tropical system weakens as the upper circulation is slanted away from the low level center.
Tendency map displays how vertical wind shear has strengthened or weakened over the past 24 hours.
When dry air is close to the vortex center, it suppresses convective development where it entrains into the storm circulation. Dry air substantially slows storm development in intensity and size.
El Niño condition prevails when Sea Surface Temperature (SST) in the Niño 3.4 region is 0.5 °C warmer than the 30 year average. Conversely, La Niña condition prevails when SST in the Niño 3.4 region is 0.5 °C colder than the 30 year average. Neutral condition exists when SST in the Niño 3.4 region is between 0.5 °C and -0.5 °C of the 30 year average. In general, during Neutral and La Niña condition, more Atlantic hurricanes are possible due to weaker vertical wind shear. In the graph above, months are grouped in three. For example, JAS is JulyAugustSeptember..