Atlantic Hurricane Outlook for the Remainder of June

By: Dr. Jeff Masters , 4:12PM,GMT on June 20,2014

There were no tropical cyclones anywhere in the world on Friday, and none of the reliable models for forecasting tropical cyclone genesis in the Atlantic (European, GFS, and UKMET) is predicting development over the coming five days. There is a tropical disturbance off the east coast of Florida that radar out of Melbourne, Florida shows some spin to. However, satellite loops show the area of heavy thunderstorms is very limited, and there is a lot of dry air interfering with thunderstorm development. Wind shear is a moderate 10 knots. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day development odds of 10%. The disturbance will likely head northeast out to sea over the weekend.


Figure 1. Tropical disturbance off the east coast of Florida as seen at 11:15 am EDT June 20, 2014. Image credit: NASA/GSFC.

Hurricane Forecast for the Remainder of June
Vertical wind shear is predicted to be very high over most of the tropical Atlantic the remainder of June, reducing the odds of tropical storm formation. With the active thunderstorm area of the MJO predicted to remain over the Pacific Ocean the rest of June, this will favor dry, sinking air over the Atlantic, further discouraging tropical storms from forming. Sea surface temperatures (SSTs), which are close to average over the Caribbean (an anomaly of +0.1°F) and cooler than average over the Gulf of Mexico (an anomaly of -0.2°F) will do no favors for any potential June tropical storms that try to form. If development does occur in June, the most likely location would be off the east coast of Florida, between the Bahamas and Bermuda, where SSTs are slightly above average and wind shear will be lower. Storms that form in this region are typically only a threat to Bermuda.

Since the active hurricane period we are in began in 1995, six of the nineteen years (32%) did not have a named storm develop in June. I give an 80% chance that 2014 will join that list. The most recent year without a June named storm developing was the El Niño year of 2009. The highest number of named storms for the month is three, which occurred in 1936 and 1968. There were two June named storms in 2013, Andrea and Barry.


Figure 2. Predicted vertical wind shear between the 850 mb and 200 mb levels for 8 am EDT Friday, June 27, 2014, as predicted by the 00Z Friday, June 20, 2014 run of the European model. High wind shear is predicted for most of the tropical Atlantic, thanks to the presence of strong upper-level winds from the subtropical jet stream (marked with arrows.) Low wind shear (red colors) are predicted for the waters of the Bahama Islands and in the Eastern Pacific off the coast of Mexico.


Figure 3. Vertical instability over the tropical Atlantic in 2014 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability was been much lower than average during June, primarily due to dry, sinking air from aloft and outbreaks of dry air from Africa's Saharan Air Layer (SAL). Low instability reduces the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.

Have a great weekend, everyone!

Jeff Masters