MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #30
*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...THURSDAY JUNE 24 2021 1:47 PM EDT...
See area of interest sections below for multiple areas being monitored for tropical development in the Atlantic basin. These areas of interest include:
(1) Area of interest #1...tropical wave of low pressure approaching the Lesser Antilles
(2) Area of interest #2...upper vortex and surface low approaching the Azores
(3) Area of interest #3...tropical wave of low pressure that has recently exited the western Africa coast
(4) Area of interest #4...surface trough that has developed in the open central Atlantic with the support of an upper vortex in the region.
Elsewhere...the tail end of the cold front in the western Atlantic will likely leave behind a surface trough of low pressure offshore of the Carolinas over the next day or so...to be supported by the divergence zone of an upper trough fragment to also be left behind over the southeast coastal US. If the surface trough develops enough thunderstorm activity and resultant latent heat release...it could increase warm upper ridging aloft that would reduce the shearing effects of the upper trough fragment. As of this afternoon...some thunderstorm activity has increased offshore of the Carolinas...will watch to see if yet another area of interest emerges here.
AREA OF INTEREST #1...The central Atlantic tropical wave of low pressure approaching the Lesser Antilles has lost thunderstorm activity while no longer aligned with the southeastern divergence zone of the upper vortex approaching from the north. The tropical wave is also in a hostile westerly shear environment on the south side of the upper vortex that would keep any new thunderstorms that try to fire displaced to the east. Tropical cyclone formation here is not expected...and the potential for this wave to redevelop thunderstorms and bring heavy rain to the Lesser Antilles is dropping as it is no longer aligned with upper-level divergence as stated earlier. This is my final statement on this tropical wave on this blog unless it continues to be mentioned in the NHC tropical weather outlook by my next update.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 25)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-62.5W)
AREA OF INTEREST #2...The upper vortex currently in the far northeast Atlantic is expected to move south toward the Azores under the influence of the amplified upper ridge over the northwest Atlantic. A new surface frontal low has formed underneath the eastern divergence zone of the upper vortex over. Although water temps around the Azores are in the low 20 deg C range...the upper vortex may be cold enough to support thunderstorms and acquisition of tropical characteristics for the surface frontal low. However I maintain very low 5% odds of subtropical development for two reasons:
(1) The 200 mb height of the upper vortex is 1200 dekameters...would like to see a colder upper vortex with a height of below 1200 dekameters for more confidence in subtropical development at these water temps.
(2) The latest forecast track keeps this system around 40N latitude...barely within the region of low-20 deg C waters.
Forecast positions in the outlook below are based on the positions of the forecast cut-off upper vortex over the next few days from today’s 0600Z GFS model run. By 72 hours the upper vortex and surface low are expected to shift west as the amplified warm northwest Atlantic upper ridge shifts east (with the warm sectors of frontal systems to eject from Canada) and steers the upper vortex and surface low westward with its south side. It is also during this time I trim off development odds down to 0% as the surface low by then will have whirled directly below the upper vortex center where there is a lack of divergence...which will cause it to gradually weaken by that time if it does not develop before then. Regardless of subtropical development or not...if the surface frontal low becomes strong enough gusty winds and coastal sea swells will be possible for the Azores within the next couple of days.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 25)...5% chance of subtropical cyclone formation (just northwest of the western Azores near 40N-30W)
IOH 48 Hr Outlook (1200Z Jun 26)...5% chance of subtropical cyclone formation (just northwest of the western Azores near 40N-30W)
IOH 72 Hr Outlook (1200Z Jun 27)...0% chance of subtropical cyclone formation (northeast Atlantic near 40.5N-35W)
AREA OF INTEREST #3...The vigorous tropical wave of low pressure that various model runs have been forecasting to develop in the eastern tropical Atlantic has now exited the western coast of Africa. The tropical wave is maintaining a surface spin and western thunderstorm bands supported by the southern outflow of the tropical upper ridge in the region. As far as forecasting is concerned...one would think that climatology would mean that this wave would not develop (i.e. it is unusual to see development in this part of the Atlantic in June due to dry Saharan air...shear...and water temps in the eastern Atlantic not yet being that warm). However it appears we are in a situation defying climatology as the western thunderstorm bands are so far shielding the low pressure spin from a recent surge of dry saharan air being swept into the Atlantic from northwestern Africa...plus the tropical wave’s current forecast track will keep it over 26+ deg C warm water...and the tropical upper ridge in the region will remain in place and keep wind shear low. I have slighlty raised my peak odds of development from 40% to 50% for the following reasons:
(1) Three of the four major computer models (GFS...CMC...NAVGEM) continue to develop this tropical wave at some point...with the 0600Z GFS showing develolpment sooner rather than later...while the CMC and NAVGEM prefer to develop this wave just after the 5-day window. It is interesting to note that the ECMWF was the only model yesterday showing development but now has dropped showing development entirely as of 0000Z...while the other three models have risen to the occassion and shown development.
(2) The tropical wave is forecsat to remain on the south side of the tropical upper ridge axis in the region...where the upper wind direction is easterly. This will tend to keep the strongest thunderstorms on the west side of the wave's spin...which may help to protect the spin from any dry saharan air to the north and west.
(3) The tropical wave has not become better organized...therefore I think only a slight rise in development odds is needed
It will be an interesting few days to see if this wave actually goes on to develop and defy climatology...stay tuned.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 25)...10% chance of tropical cyclone formation (eastern Atlantic near 8.5N-20.5W)
IOH 48 Hr Outlook (1200Z Jun 26)...30% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-25.5W)
IOH 72 Hr Outlook (1200Z Jun 27)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-30.5W)
IOH 96 Hr Outlook (1200Z Jun 28)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-35.5W)
IOH 120 Hr Outlook (1200Z Jun 29)...50% chance of tropical cyclone formation (central tropical Atlantic near 10.5N-41W)
AREA OF INTEREST #4...The central Atlantic upper vortex shearing area of interest #1 appears to be seeding its own area of interest near 25N latitude and between 50W and 55W longitude...where rotating showers and thunderstorms as well as a surface trough of low pressure have developed underneath a pocket of supporting divergence on the east side of the upper vortex. ASCAT-B and ASCAT-C descending passes suggest a surface wind shift (trough) signature a little further north...near 28N latitude...whereas the CIMSS 850 mb vorticity product (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=) suggests some low-level spin associated with the surface trough near 25N-55W. With some signatures showing up in the surface ASCAT and CIMSS products...I have declared another area of interest in this region. The upper vortex and surface trough are expected to move westward in tandem over the next 24 hours while the northwest Atlantic upper ridge and Atlantic surface ridge provide steering...which will potentially keep the surface trough aligned with the divergence zone on the east side of the upper vortex. This is when I show odds of tropical cyclone formation above 0%...but keep odds low as none of the computer models forecast development here. By 48 hours the upper vortex is expected to stall while reaching the end of its steering from the upper ridge...while the expansive Atlantic surface ridge keeps the surface trough going westward. This will push the surface trough directly below the upper vortex center where there will be a lack of upper divergence...and this is when I drop odds of development to 0%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 25)...10% chance of tropical cyclone formation (central Atlantic near 26N-59W)
IOH 48 Hr Outlook (1200Z Jun 26)...0% chance of tropical cyclone formation (western Atlantic near 26N-64W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...
**For area of interest #1...no tropical cyclone formation shown
**For area of interest #2...surface frontal low arrives just west of the Azores by 48 hours....drifts east into the Azores by 72 hours...turns west-northwest and reaches 42N-35W by 120 hours.
**For area of interest #3...low pressure spin of tropical wave reaches 10N-26W at 60 hours...low pressure spin dissipates near 10N-37.5W at 102 hours...as tropical wave approaches Trinidad and the southern Lesser Antilles in long range (168 hours) tropical cyclone formation is suggested.
**For area of interest #4...no tropical cyclone formation shown
0000Z ECMWF Model Run...
**For area of interest #1...no tropical cyclone formation shown
**For area of interest #2...surface frontal low arrives just west of the Azores by 48 hours while a tight subtropical circulation develops within its south side...subtropical circulation becomes the dominant and swings north to 42.5N-30W by 72 hours...turns west and reaches 41.2N-36W at 96 hours...drifts east and reaches 41.2N-35W by 120 hours.
**For area of interest #3...no tropical cyclone formation shown
**For area of interest #4...no tropical cyclone formation shown
0600Z GFS Model Run...
**For area of interest #1...no tropical cyclone formation shown
**For area of interest #2...surface frontal low arrives just northwest of the Azores by 30 hours and remains stationary through 66 hours...drifts northwest to 41.5N-35.5W by 120 hours.
**For area of interest #3...compact tropical depression or storm suggested near 10.5N-24W at 54 hours...the compact tropical cyclone gradually weakens while reaching 10.5N-43W by 120 hours.
**For area of interest #4...no tropical cyclone formation shown
0600Z NAVGEM Model Run...
**For area of interest #1...no tropical cyclone formation shown
**For area of interest #2...surface frontal low arrives just northwest of the Azores by 36 hours....drifts slowly north out ahead of cold front to be driven into the far north Atlantic by the current central Canada frontal cyclone and reaches 45N-30W by 120 hours.
**For area of interest #3...no tropical cyclone formation shown through 120 hours...as wave crosses the southern Lesser Antilles by 168 hours some development is suggested.
**For area of interest #4...no tropical cyclone formation shown