Summary: I am forecasting above average tropical storm and hurricane season due to a combination of La Nina conditions becoming neutral ENSO conditions, the forecast of an active Western African Monsoon, the forecast of above average ocean water temperatures and the possibility of lower than average wind shear conditions. Unlike last year, I think the 2021 may feature much more in the way of long-track tropical storms and hurricanes.
The Numbers: 16 Named Storms, 8 of those storms becoming Hurricanes and 4 of those hurricanes becoming Major Hurricanes (Category 3 or higher on the Saffir-Simpson scale).
Accumulated Cyclone Energy (ACE) Index Forecast: I am forecasting an ACE index this year of 150. This number basically says that I expect that overall activity in the Atlantic will be above average.
ENSO Conditions: Weak La Nina conditions currently exist across the Pacific and it appears quite likely that the ENSO state will “warm” to neutral conditions by early this summer. Much of the ENSO guidance then forecast that ENSO conditions will remain neutral throughout this summer into this autumn.
Based on everything that I have looked at, I think that we should see neutral ENSO conditions throughout the 2021 Atlantic Hurricane Season. With that said, ENSO forecasts this time of year can be highly inaccurate.
Sea Surface Temperatures: Sea surface temperatures across the Atlantic Basin look very similar to what they looked like at this time last year. Across the Western Atlantic and Caribbean (west of 55 West Longitude) ocean water temperatures are warmer than average. Across the central and eastern Tropical Atlantic, sea surface temperatures are below average.
One difference this year as compared to last year is in the Gulf of Mexico and right along the East Coast of the United States. Ocean water temperatures are below average in the western and northwestern Gulf of Mexico, but above average across the southern and eastern Gulf of Mexico. In addition, below average ocean water temperatures are occurring right along the East Coast of the United States. These below average temperatures are due to the very cold February and is likely very temporary & I expect to see these water temperatures warm significantly in the coming weeks.
One of the keys in determining how active/inactive the hurricane season will be is how much will the deep tropics (south of 25 North Latitude) warms up during April, May and June. It should be noted that at this time in 2017, 2018, 2019 and 2020, the Atlantic Main Development Region was running a little below average in sea surface temperatures, but this pattern reversed during the hurricane season leading to a much more active season than what was originally thought.
I think that it is likely that the deep tropics will seeing above average ocean water temperatures, much like what we have seen during the last 4 hurricane seasons, during July, August and September. In addition, it looks like the Western African Monsoon will be active this year leading to the development of some strong tropical waves moving off of Africa.
Analog Years: These are the analog years that seem to be a close match right now to what the 2021 hurricane season may be like. They are 1899, 1950, 1956, 1996, 1999, 2008 & 2012.
Based on what I am seeing comparing the current weather pattern to the analog years I have listed, I am putting special emphasis on 1996 and 2012 as analog years for this season. This means that the Southeast US Coast, especially along the North and South Carolina coast, could be at particular risk this season for a landfalling tropical storm or hurricane. More on that in my landfall threat forecast.
This is our “hot spot” map which shows which areas were impacted the most during the 7 analog years I have listed:
Wind Shear Forecast: A majority of the seasonal model guidance are forecasting below average wind shear across a large part of the Atlantic, Caribbean and Gulf of Mexico during much of the hurricane season. Should this come to pass, it would mean a favorable environment for tropical storm and hurricane formation and intensification.
Weather Pattern Forecast: Current seasonal guidance are pointing towards the possibility that a persistent upper level trough may set up near the central Great Lakes region along about 82-84 West Longitude in about June and July and then push westward towards the northern Plains states near about 100 West Longitude as we get into August and September. At the same time this is occurring, a persistent upper level high pressure ridge may set up near Nova Scotia and Newfoundland in July and then push westward into southern Quebec province and northern parts of New England by August and September.
What this means is that should we see any June or July tropical systems, the upper level pattern may be such that the East Coast of the United States may be open to an impact. It also potentially means that May, June and July could be quite wet and stormy across a large part of the Eastern United States.
During August and September, a weather pattern of a trough of low pressure over the northern Plains States and a high pressure ridge over the Northeastern United States could open up the eastern and central Gulf States as well as the Bahamas and the Florida Peninsula to possible tropical storm and hurricane threats.
Landfall Threat Forecast: The area I am most concerned about this season for a tropical storm or hurricane impact is a corridor from the northeastern Caribbean west-northwestward through the Bahamas, the eastern and central Gulf Coast, the Florida Peninsula and US Southeast Coast, including Georgia, South Carolina and North Carolina. The analog data and the upper level weather pattern forecasts indicate that a high pressure ridge over either the northeastern United States or Atlantic Canada could guide any storms towards this corridor.
I do think that we could see some long-track storms that form over the eastern Atlantic and then head westward. Based on what I am seeing the data though, the turn towards the northwest may occur just before the Caribbean, which as I just mentioned could put the northeast Caribbean at particular risk this season.
The central and western Caribbean may see below average activity this season as most of the seasonal guidance points towards below average to well below average rainfall throughout this summer and autumn.
For all of the other areas across the Atlantic, Caribbean and Gulf of Mexico, including the western Gulf Coast, the Mid-Atlantic and northeastern United States and the eastern and southeastern Caribbean – about average impact risk is expected at this time. Any small fluctuations in the upper level weather pattern at the “wrong” time could put other areas not highlighted at risk.
One Word Of Caution: I do want to say that there is the very slight possibility that this upcoming season could end up resembling 2006 or 1956. Both years began with La Nina conditions, but then quickly warmed to El Nino conditions by the peak of the hurricane season. This led to a below average season for both 1956 and 2006. I don’t think that this will happen as there is pretty strong evidence in the data that suggests we will either “warm” into neutral ENSO conditions or even remain in a weak La Nina state. In fact, we may not see our next El Nino until 2022 or even 2023. With that said, the very slight possibility of a El Nino forming is something that I’ll definitely be watching for in the data.
Finally, we will begin sending out daily tropical weather discussions for the 2021 Atlantic Hurricane Season on Saturday, May 1st.
2021 Atlantic Tropical Cyclone Names: