Tropical Wave 94L Approaching The Bahamas Not Likely to Develop

July 21, 2019, 11:38 AM EDT

Above: Invest 94L approaching the central Bahamas, as seen at 10:40 am EDT Sunday, July 21, 2019. Image credit: NOAA/RAMMB.

A tropical wave located a few hundred miles east of the central Bahama Islands was designated 94L by the National Hurricane Center (NHC) on Sunday morning. This wave was headed west to west-northwest at 10 - 15 mph, and is likely to bring rains of 1 – 2” to the Bahamas beginning on Sunday night, and 1 – 2” to portions of Florida beginning on Monday night. However, development of 94L into a tropical depression is unlikely.

Favorable parameters for development of 94L into a tropical depression included sea surface temperatures (SSTs) near 29.5°C (85°F) and moderate wind shear near 10 knots. Unfavorable for development was the very dry atmosphere 94L was embedded in, with a mid-level relative humidity near 40%--caused by the dry air from the Saharan Air Layer. Satellite images on Sunday showed that the wave had plenty of spin, but only a small amount of heavy thunderstorms, due to dry air.

Forecast for 94L

The 12Z Sunday run of the SHIPS model predicted that SSTs would increase to a very warm 30°C (86°F) by Wednesday and wind shear would be light to moderate, 5 – 10 knots. During this time, the atmosphere was predicted to stay dry, with a mid-level relative humidity of 45 – 55%. These conditions may allow some slow development of 94L. None of our top three models for predicting tropical cyclone development--the GFS, European, and UKMET models--predicted development of 94L into a tropical depression with their 0Z Sunday runs. The disturbance also had very little support for development from the 0Z Sunday GFS and European model ensemble forecasts.

94L will turn more to the northwest on Tuesday and Wednesday, and is likely to get absorbed on Thursday by a cold front expected to push off the U.S. East Coast. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave 94L 2-day and 5-day odds of development of 10% and 20%, respectively. The next name on the list of Atlantic storms is Chantal. As of late Sunday morning, there were no hurricane hunter flights scheduled to investigate 94L.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995, and flew with the NOAA Hurricane Hunters from 1986-1990.

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