An area of disturbed weather in the extreme southern Caribbean off the coast of Nicaragua (Invest 90L)
has changed little since Wednesday, but is still expected to develop into a tropical depression by early next week as it meanders erratically. Satellite loops
on Thursday morning showed that 90L had a modest amount of rotation, but heavy thunderstorm activity was sparse and not showing any increase. 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 parked in this area for multiple days could cause significant flooding and landslides. For example, Tropical Storm Gamma
of 2005, with top winds of just 50 mph, stalled just north of Nicaragua on November 18 - 20, causing at least 37 fatalities in Honduras and Belize.
Our three reliable models for prediction of tropical storm genesis—the European, GFS and UKMET models—continued to forecast in their 0Z Thursday operational runs that 90L would develop into a tropical depression by early next week. About half of the 50 forecasts from the 0Z Thursday European model ensemble predicted that 90L would eventually become Tropical Storm Otto. However, only 4% of these forecasts showed 90L becoming a hurricane. About 85% of the 20 GFS ensemble members from the 0Z Thursday forecast produced a Tropical Storm Otto. In their 7 am EST Thursday Tropical Weather Outlook,
NHC gave 90L 2-day and 5-day development odds of 20% and 70%, respectively—a decrease of 10% from the odds given Wednesday morning. The Hurricane Hunters are on call to potentially investigate 90L on Friday afternoon.
We’ll have a new post early this afternoon on the NOAA global climate summary for October.