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(T. F. “Storm” Walsh III)
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SET YOUR CLOCKS ONE HOUR AHEAD SUNDAY, MAR. 11, 2018
Good evening everyone!
This is another preliminary outlook to the upcoming 2018 hurricane season. From here on out, I will try to post a preliminary outlook near the beginning of each month, until the season kicks off June 01, 2018
The following factors will be important players on the field in determining how busy the season could be:
Gulf of Guinea anomalies
Indian Ocean Dipole
I’ve taken today to analyze updated ENSO forecast information and wanted to post an update regarding my 2018 hurricane season outlook forecast. Based on analysis of the most current updates in climate modeling, the “consensus” still calls for ENSO neutral conditions for the 2018 Atlantic Hurricane Season. Analysis today of the climate models reveal the majority of modeling has trended toward neutral “warm bias” ENSO forecast conditions. The UKMET and CFSv2 Nino Plume forecasts appear to be the only models indicating La Nina to Neutral cold bias conditions. The following are the climate modeling Nino 3.4 plumes.
NCEP CFS v2
The following is a breakdown of ALL of the climate models, average of the dynamic modeling, average of the statistical modeling, and average of ALL of the models combined.
The Atlantic has cooled slightly, however we are just coming off a 1 month run of a fairly strong positive NAO (North Atlantic Oscillation). A strong positive NAO indicates higher than average pressures associated with the Azores-Bermuda high, which increases trades in the Atlantic, creating upwelling of colder water in the Atlantic basin.
CURRENT NAO AND FORECAST
GFS AND ECMWF NAO FORECAST
IF the current NAO forecast is correct, I would expect to see the Atlantic basin recover with slow warming during the next couple of weeks.
One item of interest is, the possible cooling in the Gulf of Guinea. This generally plays a role in rainfall over Guinea, or in some cases, rainfall over the West African Sahel region. Let’s look at the 2016 and 2017 hurricane seasons. The Gulf of Guinea was pretty much showing warmer anomalies, albeit weaker warm anomalies in 2017. A warmer Gulf of Guinea, in general, keeps the ITCZ pretty much suppressed further south over the African continent. This causes the Sahel region to remain drier with average or below average rainfall. Given the pressure gradient created by colder anomalies in the Gulf of Guinea, in relation to the hotter African continent (higher pressure now over the Gulf of Guinea, lower pressures north), the ITCZ is pushed further north, and can reach into the Sahel region. This allows for more rainfall over the Sahel, which in turn helps to cut down on SAL outbreaks and their severity. This increases the chance of a greater number of tropical waves, and an increase in intensity of these waves. Hence, an added possibility of an above average season.
GULF OF GUINEA
2012 GULF OF GUINEA COLD ANOMALY
CURRENT SST ANOMALIES
Looking at the current forecast SST anomalies, we could see anywhere from “neutral”, to “neutral cold bias” conditions. Based on the modeling, it appears the Atlantic basin becomes warmer, but north of the MDR.
The following are forecasts for SST anomalies and probabilities:
CFSv2 SST ANOMALY FORECAST
The IOD (Indian Ocean Dipole), (to my understanding from previous readings) has an effect on the WAM (West African Monsoon) circulation, in that a negative IOD has the tendency not to disrupt the WAM, which plays a part in rainfall, and anomalous westerly surface winds at near 10N latitude. We did observe the WAM a few times near the peak of the 2017 season, however if my understanding of this feature is correct, the WAM is more pronounced during a negative IOD. The 2017 season witnessed a “neutral” to “positive” IOD phase. The current forecast indicates the IOD may remain neutral. This may or may not be a slightly negating factor for a busy season, however the other factors mentioned in this update, would be positive for an above average season.
Positive: cooler in the tropical eastern Indian Ocean and warmer in the tropical western Indian Ocean.
Negative: warmer in the tropical eastern Indian Ocean and cooler in the tropical western Indian Ocean.
CURRENT IOD FORECAST
The AMO (Atlantic Multi-decadal Oscillation) is basically whether or not the Atlantic Basin SST’s and anomalies are above average or below average based on climatology. Currently, the AMO is in a weak positive state. This means SST anomalies continue to be warmer than the average, based on climatology. A positive AMO is conducive for an above average season, when coupled with other positive factors. One possible negating factor could be the premise of warmer SST’s being forecast to remain north of the MDR, as seen in the SST anomaly projections above.
Analysis of the CFSv2 u200 – u850 maps still indicate wind shear over the Atlantic for this upcoming season is to remain below average, indicated by the blue shading:
CFSv2 WIND SHEAR FORECAST
Based on the values and trend of the current Nino Plume forecasts with the majority of the climate models trending warmer, warmer overall model averages, coupled with the ONI (Oceanic Nino Index), I had to make a slight change to my preferred analog years. Based on the same method I used in my last update, I have lowered my forecast totals slightly. Again, if we stay in a weak La Nina, or shift to a neutral cold bias, the outlook numbers should reflect totals the higher end. IF we shift to a warm bias, the outlook should reflect totals near the lower end. The following update is as follows:
TOTAL STORMS: 13-18
MAJOR HURRICANES: 3-5
I intend to hopefully have a forecast synopsis sometime tomorrow, for the next coastal/offshore system slated for Monday, March 12, 2018.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS