2021 ATLANTIC HURRICANE SEASON SUPPLEMENTAL UPDATE…ISSUED JUN. 21, 2021…7:30 P.M. EDT

2021 ATLANTIC HURRICANE SEASON SUPPLEMENTAL UPDATE…ISSUED JUN. 21, 2021…7:30 P.M. EDT


Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(T. F. “Storm” Walsh)

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Greetings to everyone!
Please be aware, even though I do not post every night, rest assured I am continuously monitoring various areas for any significant weather.  I will be taking Sundays off (family time), unless we have active systems that may be posing a threat (i.e. Tropical, Winter Weather, Coastal Storms, etc.).

Before I go into the update, I wished to point something out.  I’m sure some of you out there have seen a select few referencing whether or not the year 2005 would be used as an analog year.  Basically, No.  One of the main reasons is, the SST anomaly maps are two totally different critters.
JUNE 20, 2021 SSTA
oisst_anom_1d_tropatl_2021062000
JUNE 20, 2005
oisst_anom_1d_tropatl_2005062000
You will notice the SST anomalies for 2005 indicate very warm anomalies near 50.0N, and northward, with colder anomalies from 30.0N to 50.0N.  Then you’ll note very warm anomalies over the MDR (Main Development Region…10.0N to 20.0N).  This setup is known as the Atlantic Ocean Tripole.  The warm anomalies over the extreme north would promote upward motion, or rising air over the area, providing “lift”.  The colder anomalies would be indicative of sinking air.  Once again, the warmer anomalies in the MDR would indicate lift, however the lift would be stronger due to the sinking air coming in from the north, then rising.  This produces what we term as maximum net lift, which causes high instability over the MDR.  This is one of the reasons the 2005 season was “hyper-active”.  You’ll note the opposite in the 2021 anomalies.

I will be addressing the tropical wave east of the Lesser Antilles, and the remainder of the tropics, hopefully tomorrow evening.  Bear in mind, conditions are still somewhat favorable for development around the GOMEX and of the SEUS coast close to the Bahamas, based on the MJO phase, and current 200CHI anomalies forecast maps, until July 01.

I performed a secondary analysis today of the most current forecast information from various global and climate models regarding the tropics.  Based on the parameters analyzed, the 2021 Atlantic Hurricane Season will most likely be another “active” season.

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
7.) AVERAGING OF ENSO NEUTRAL SEASONS SINCE 1995

Based on everything I analyzed, and the fact that questionable systems are being named left and right, I have decided to increase my seasonal forecast total slightly (total named storms):
STORM W PRE-SEASON FORECAST
TOTAL NAMED STORMS: 17 – 20
TOTAL HURRICANES :        7 – 9
MAJOR HURRICANES:       4 – 5

AVERAGE HURRICANE SEASON:
TOTAL NAMED STORMS: 14
TOTAL HURRICANES:         7
MAJOR HURRICANES:       3

The powers that be decided to come up with new totals for what an “average” hurricane season is. I don’t agree with it, for if and when we switch to a COLD AMO phase, statistics could change for the lower.  I won’t discuss it further, as I don’t feel like getting into “politics”

From NOAA:
Beginning with this year’s hurricane season outlooks, NOAA’s Climate Prediction Center (CPC) will use 1991-2020 as the new 30-year period of record. The updated averages for the Atlantic hurricane season have increased with 14 named storms and 7 hurricanes. The average for major hurricanes (Category 3, 4 or 5) remains unchanged at 3. The previous Atlantic storm averages, based on the period from 1981 to 2010, were 12 named storms, 6 hurricanes, and 3 major hurricanes.

I am reducing some of the graphics, as a majority of the climates models are in good agreement, however you’ll get the main idea of what the forecast climate models are getting at.

Based on analysis of the forecast ONI (Oceanic Nino Index) values from the IRI (International Research Institute) / CPC (Climate Prediction Center), the forecast calls for pretty much straight NEUTRAL ENSO conditions from now, until we get near the peak of the season, with the possibility of weak La Nina conditions showing up.  Based on the values and trend analyzed, the previous hurricane seasons which came closest to temperature, and “trend” of the values were 1996, 2001.  Based on these (analogs), the average storm totals worked out to 14 named systems, 8 hurricanes, and 5 major hurricanes.  The average for all of the NEUTRAL ENSO seasons since going into the warm AMO back in 1995, worked out to 16 named systems, 8 hurricanes and 4 major hurricanes.

The following is a good article from FSU regarding hurricane development and landfalls during the different phases of ENSO:
https://climatecenter.fsu.edu/topics/tropical-weather/regional-effects-of-enso-on-us-hurricane-landfalls#Tropical%20Cyclone%20Steering

The ENSO plumes forecast still indicates NEUTRAL conditions with a slightly cold bias, however models tend to indicate a possible return to a weak La Nina pattern near the peak of the season.  Keep in mind, the effects of this take a little time to teleconnect between ocean and atmosphere :
CFSv2 FORECAST
nino34Sea
BOM FORECAST
20210608.sstOutlooks_nino34

NMME FORECAST
nino34.rescaling.NMME


IRI / CPC FORECAST
figure4
Having analyzed the following SST anomaly 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. , although the MDR seems to appear cooler in the anomalies.  This could imply close to the same development pattern in which we had numerous close in development type systems.  The SST anomalies forecast maps are from the CFSv2 with the NMME climate models linked in order to view different members
CFSv2 SST ANOMALIES (CLICK ON IMAGES)
glbSSTSeaInd1
glbSSTSeaInd2
Looking at the forecast anomalies for the Gulf of Guinea, it appears the GOG remains warm.  This could be a little bit of a game changer, as a warmer GOG has the tendency to keep the ITCZ further south, meaning less rainfall for the Sahel region, which could mean more African dust (SAL).
GULF OF GUINEA
2021-02-10-gulf-of-guenea-piracy-map

Another item in the forecast, regarding Sea Surface Temperature Anomalies, is the IOD (Indian Ocean Dipole).  The climate models which track this, indicate the IOD to go neutral to negative phase, with a good majority of the ensemble members heading toward a 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.  The positive IOD phase also acts as an El Nino affect over Africa and portion of the Atlantic ocean by inducing wind shear.  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-positive

IOD NEGATIVE PHASE
iod-negative
The following is an excerpt from an abstract written by Kimberly M. Wood (et.al.), referencing the IOD:

The 2019 Atlantic hurricane season exhibited above‐average Accumulated Cyclone Energy—60% of which was produced by Hurricanes Dorian and Lorenzo. Most tropical cyclone (TC) activity was concentrated in a ~6‐week period from late August to early October. During the early part of the season, relatively TC‐unfavorable conditions persisted in the main development region (MDR). The MDR environment became largely favorable in September, followed by an abrupt shift back to less conducive conditions in October coincident with a strongly positive Indian Ocean Dipole (IOD). The IOD produced an El Niño‐like teleconnection pattern observed through 200‐hPa velocity potential anomalies.  In the subtropical Atlantic, above‐average sea surface temperatures persisted for much of the season, which may have contributed to increased activity at higher latitudes. Given the neutral El Niño‐Southern Oscillation conditions during the 2019 hurricane season, our study highlights the need for further analysis of IOD impacts on Atlantic TC activity.

IF the climate modeling is correct, and the IOD goes neutral to 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
20210608.sstOutlooks_iod
UKMET IOD FORECAST
iod_anom_20210601
NASA GEOS IOD FORECAST
idm_jun2021_plume_S2S

With the forecast of a neutral ENSO, the CFSv2 is showing normal (or average) wind shear over the Atlantic basin, which is another slightly enhancing factor for the hurricane season.  However, the shear anomalies are not as favorable as they were from the Feb. update.  Based on this fact, I decided not to change the hurricane totals at the moment
CFSv2 CURRENT SEASONAL u200 – u850 (WIND SHEAR) FORECAST
AtludifSea
You may direct any questions this season by contacting me personally, ANYTIME, at: [email protected]

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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