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(T. F. “Storm” Walsh)
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I performed analysis today of the most current forecast information from various global and climate models. Based on the parameters analyzed, the 2021 Atlantic Hurricane Season COULD be another “above average” season. As always, this forecast is subject to change, as forecast models continue to update each month, between now and June 01. However, with the current available information, it looks like another busy season. Although analysis of forecast Oceanic Nino Values indicate slightly warmer anomalies, the anomalies are forecast to remain negative, and currently indicate neutral conditions. After comparing these values to past trends in the current ONI chart, the analog years I averaged tend to indciate a a slight decrease in storm totals by 1 storm. However, I am not making any change to my pre-season forecast totals, given that 2 of the forecast items are showing signs of being very favorable, especially by the “peak” of the season. This would be IRT the wind shear forecast and IOD (Indian Ocean Dipole).
The following is my PRE-SEASON outlook forecast for the upcoming 2021 Atlantic Hurricane Season:
STORM W PRE-SEASON FORECAST
TOTAL NAMED STORMS: 15 – 17
TOTAL HURRICANES : 7 – 9
MAJOR HURRICANES: 3 – 4
AVERAGE HURRICANE SEASON:
TOTAL NAMED STORMS: 12
TOTAL HURRICANES: 6
MAJOR HURRICANES: 3
Forecast parameters used in this synopsis include the following:
1.) CLIMATE MODEL ENSO PLUME FORECASTS
2.) SST ANOMALY FORECAST
3.) IOD (Indian Ocean Dipole) FORECAST
4.) WIND SHEAR FORECAST
5.) ONI (Oceanic Nino Index) FORECAST TEMPERATURES AND TRENDS
6.) AVERAGING OF CHOSEN ANALOG YEARS
Based on analysis this afternoon of current forecast ENSO plumes from global and climate modeling, the models seem to indicate ENSO NEUTRAL to ENSO NEUTRAL COLD BIAS. As a rule of thumb, the cooler NINO 3.4 becomes, the more favorable conditions over the Atlantic become for storm development. The following are ENSO plume forecast charts analyzed today:
NCEP CFSv2 ENSO PLUMES FORECAST
BOM (AUSTRALIA BUREAU OF METEOROLOGY)
IRI / CPC
The following SST anomalies forecast maps are from the CFSv2 and NMME climate models. The NMME maps are linked to show the various ensemble members.
CFSv2 SST ANOMALIES
Having analyzed the above maps, the SST anomaly pattern looks very similar to the pattern of 2020, in which warmer SST anomalies were north of 20N, and closer to the U.S. This could imply the same development pattern in which we had numerous close in development type systems.
It was once again noted that most of the models indicate the Gulf of Guinea to turn neutral to cooler. This was forecast to occur in the 2020 season, however didn’t really come to fruition. SHOULD this occur however, and cooling becomes significant, a shift northward in the ITCZ/Monsoon Trough could occur, and possibly bring greater rainfall to the Sahel region, which would aid in a reduction in the SAL.
Another item in the forecast, regarding Sea Surface Temperature Anomalies, is the IOD (Indian Ocean Dipole). The updated forecast from the climate modeling tends to show the IOD staying fairly steady, up until MAY. The 3 climate models which track this, indicate the IOD to go a fairly strong negative phase. During a positive IOD phase, you’ll notice the “Walker” circulation allowing for an increase in convection and rain near east Africa. The rising air causes lower pressure and precipitation at the ocean surface. You’ll see on the eastern side of the circulation, air sinks to the surface, causing higher pressure at the surface and drier conditions. This exact flow happens on the western portion of the circulation near the African east coast. The air rises, and as it reaches the upper portion of the atmosphere, it cools, then begins to sink (higher pressure). As this air in the upper atmosphere sinks, it compresses and heats, drying out the air, hence the “lack” of convection for easterly waves over central Africa. A negative IOD phase has the opposite effect. As the air “sinks” over the western Indian Ocean, it spreads out over the surface, and across eastern Africa. The pattern then continues with the air “rising” over central Africa, allowing for, or aiding in the formation of convection.
IOD POSITIVE PHASE
IOD NEGATIVE PHASE
IF the climate modeling is correct, and the IOD goes negative as shown, there could be an increase in tropical wave activity during the Cape Verde season, not unlike what happened last season.
IOD FORECAST FROM BOM
IOD FORECAST FROM UKMET
NASA GEOS IOD FORECAST
With the forecast of a neutral cold biased to neutral ENSO, the CFSv2 is showing well below normal wind shear over the Atlantic basin for the season, which is another enhancing factor for the hurricane season.
CFSv2 CURRENT SEASONAL u200 – u850 (WIND SHEAR) FORECAST
Based on analysis of forecast ONI values from the IRI (International Research Institute), which uses 26 different climate models, I came up with the following past hurricane seasons as analog years: 1989, 1996, 2001, and 2008. I determined this from ONI values and / or value trends based on the average of ALL the climate models, comparing them to the CPC ONI chart. The IRI provides an average of the Dynamical models, Statistical models, and an average of ALL 26 models output. Based on those years, the average worked out to 14 storms, 8 hurricanes, and 4 major hurricanes. The following is an explanation of the ONI from the HDX (Humanitarian Data Exchange)
Monthly Oceanic Nino Index (ONI):
The Oceanic Niño Index (ONI) has become the de facto standard that the National Oceanic and Atmospheric Administration (NOAA) uses to identify El Niño (warm) and La Niña (cool) events in the tropical Pacific. It is the three month mean SST anomaly for the El Niño 3.4 region (i.e., 5°N-5°S, 120°-170°W). Events are defined as five consecutive overlapping three month periods at or above the +0.5°C anomaly for warm (El Niño), events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into Weak (with a 0.5 to 0.9 SST anomaly), Moderate (1.0 to 1.4) and Strong (≥ 1.5) events. For an event to be categorized as weak, moderate or strong. it must have equaled or exceeded the threshold for at least three consecutive overlapping three month periods.
IRI ONI FORECAST
NOAA CPC ONI CHART
You may direct any questions this season by contacting me personally, ANYTIME, at: email@example.com
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
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