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Invest 90L Off the Coast of Nicaragua Less Organized

By: Jeff Masters 2:05 PM GMT on November 18, 2016

An area of disturbed weather in the extreme southern Caribbean off the coast of Nicaragua (Invest 90L) is struggling to develop, but is still expected to become a tropical depression by early next week as it meanders erratically. Satellite loops on Friday morning showed that 90L had a modest amount of rotation, but heavy thunderstorm activity had decreased since Thursday and was sparse and disorganized. The disturbance had plenty of moisture to work with (about 70% relative humidity at mid-levels of the atmosphere), and water vapor satellite imagery showed no large-scale areas of dry air that 90L might have to contend with. Wind shear was marginally favorable for development, near 20 knots. Sea surface temperatures (SSTs) were very warm, near 29.5°C (85°F), which was about 1°C (1.8°F) above average.

Figure 1. Latest satellite image of 90L.

Track forecast: 90L a heavy rain threat to Central America
Steering currents are weak in the region, and 90L will not move much over the next five days. Heavy rains over Panama, Costa Rica and Nicaragua are a major concern from 90L, as even a weak tropical depression or tropical storm meandering in this area for multiple days could cause significant flooding and landslides.

Our three reliable models for prediction of tropical storm genesis—the European, GFS and UKMET models—continued to forecast in their 0Z Friday operational runs that 90L would develop into a tropical depression by early next week. About three-quarters of the 50 forecasts from the 0Z Friday European model ensemble predicted that 90L would eventually become Tropical Storm Otto. However, only 6% of these forecasts showed 90L becoming a hurricane. About 85% of the 20 GFS ensemble members from the 0Z Friday forecast produced a Tropical Storm Otto. In their 7 am EST Friday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day development odds of 10% and 60%, respectively—a decrease of 10% from the odds given Thursday morning. The Hurricane Hunter mission scheduled for Friday afternoon has been canceled, and is scheduled to fly on Saturday afternoon, if necessary.

We’ll have a new post early this afternoon on some crazy happenings in the Arctic.

Jeff Masters


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