MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #27

*******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.**********

...MONDAY JUNE 21 2021 10:10 PM EDT...

See Claudette section below for an update on the tropical storm…which is offshore of the northeast US and Nova Scotia. See area of interest sections below for additional areas being monitored for development.

Elsewhere…conditions in the eastern tropical Atlantic have improved again for potential development as dry Saharan air has been weakened by tropical waves of low pressure emerging from Africa that are producing rotating thunderstorm clusters. Models forecast that the upper ridge in the region keeping shear low and outflow high will be in place for the next several days…and during today’s 1200Z model cycle the GFS and NAVGEM hinted at development here in the 4 to 5 day window…and the CMC and ECMWF at least showed a strong tropical wave emerge from Africa in that same timeframe. Therefore will be keeping an eye on this region in the coming days.

TROPICAL STORM CLAUDETTE...As forecast…Claudette regained tropical storm status this morning as the circulation continued northeast in track…and entered the warm Gulf Stream waters of the western Atlantic from the coast of North Carolina. The atmosphere around Claudette has warmed by the surface southerly flow ahead of current central Canada frontal low. This has resulted in warm upper ridging forming over Claudette with low shear and upper outflow which has aided the tropical storm…and as of 5 PM EDT Claudette reached a strength of 45 mph maximum sustained winds. This will likely be the peak intensity of Claudette as the storm is moving into cooler water…and by tomorrow as Claudette approaches Atlantic Canada (Nova Scotia and Newfoundland)…I currently forecast a weak remnant low as the upper trough supporting the central Canada frontal low will be too far west to aid Claudette’s remnants with its eastern divergence zone.

Quickly passing coastal sea swells and rip currents as well as offshore choppy seas are likely for a few more hours for the United States New England coast…as well as Canada’s Nova Scotia coast. Based on the above outlook…the chances for Claudette to kick up the seas on coastal Newfoundland is low due to forecast weakening….and also the chance for Claudette to bring winds directly to Newfoundland and Nova Scotia is also low as a result of the forecast weakening.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1800Z Jun 21)…45 mph maximum sustained wind tropical storm centered offshore of the US New England Coast at 37.5N-72.1W

IOH 24 Hr Forecast (1800Z Jun 22)…Remnant low centered just offshore of eastern Nova Scotia at 44.5N-61.2W

AREA OF INTEREST #1…The National Hurricane Center has recently begun monitoring a tropical wave of low pressure in the central Atlantic for further development as the wave has taken advantage of low shear and upper outflow beneath low-latitude upper ridging currently present…resulting in it keeping a small pocket of showers and thunderstorms with rotation despite an abundance of dry Saharan air just to the east. Normally this time of year tropical waves in this region are kept in check by either wind shear or the Saharan air layer…and perhaps the dry air layer is finally affecting this wave as the thunderstorm activity is less abundant compared to this morning. Therefore I assign low short term odds of development of 10% for the next 24 hours.

The southwest portion of the current northwest Atlantic upper trough will soon be pushed southward toward this tropical wave by the amplifying upper ridging over Claudette (this ridging is supported by the warm sector of the current central Canada frontal low). This portion of the upper trough will drive increasing westerly shearing winds over the wave by 48+ hours…and thus I trim odds of development down to 0% by 72 hours. The chances that this wave will be a tropical cyclone (depression or storm) while passing the southern Lesser Antilles between 48 and 72 hours is very low…however the wave may bring enhanced rainfall if the wave’s thunderstorms becomes enhanced by the eastern divergence zone of the arriving upper trough energy.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z Jun 22)…10% chance of tropical cyclone formation (east of the Lesser Antilles near 10.5N-55W)

IOH 48 Hr Outlook (1800Z Jun 23)…5% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 11N-60W)

IOH 72 Hr Outlook (1800Z Jun 24)…0% chance of tropical cyclone formation (southeastern Caribbean Sea near 11.5N-65W)

AREA OF INTEREST #2…The northeast portion of the current northwest Atlantic upper trough is forecast to become a cut-off cold upper vortex that becomes pushed southeastward into the Azores by the amplifying upper ridging over Claudette (this ridging is supported by the warm sector of the current central Canada frontal low). The surface frontal low currently supported by the divergence zone of the upper trough is forecast to regenerate southeastward while supported by the divergence zone of the upper vortex…or alternatively the current frontal low will dissipate while a new one forms to the southeast. Although water temps around the Azores are in the low 20 deg C range…the upper vortex could become cold enough to support thunderstorms and acquisition of tropical characteristics for the surface frontal low to be supported by the upper vortex. However I have low 10% odds of subtropical cyclone formation as the 200 mb height of the upper vortex is forecast to be around 1200 dekameters…would like to see a colder upper vortex with a height of below 1200 dekameters for more confidence in subtropical development. Forecast positions in the Outlook below are based on the positions of the forecast cut-off upper vortex over the next five days from today’s 1200Z GFS model run.

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 in the 3 to 5 day timeframe.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z Jun 22)…0% chance of subtropical cyclone formation (north Atlantic near 51N-35W)

IOH 48 Hr Outlook (1800Z Jun 23)…0% chance of subtropical cyclone formation (northeast Atlantic near 50N-26W)

IOH 72 Hr Outlook (1800Z Jun 24)…0% chance of subtropical cyclone formation (northeast Atlantic near 44N-26W)

IOH 96 Hr Outlook (1800Z Jun 25)…10% chance of subtropical cyclone formation (western Azores near 39N-30W)

IOH 120 Hr Outlook (1800Z Jun 26)…10% chance of subtropical cyclone formation (Azores near 38.5N-27.5W)

...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)

1200Z CMC Model Run...

**For Tropical Storm Claudette…opens to a surface trough while making landfall over eastern Nova Scotia at 42 hours

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives to the western Azores by 90 hours….cyclonically loops to a location just west of the Azores by 120 hours.

1200Z ECMWF Model Run...

**For Tropical Storm Claudette…opens to a surface trough while moving into Atlantic Canada by 48 hours

**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 96 hours….cyclonically loops to a location just west-southwest of the Azores by 120 hours.

1200Z GFS Model Run...

**For Tropical Storm Claudette…opens to a surface trough while making landfall over western Nova Scotia at 27 hours

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives over the Azores by 99 hours….remains stationary through 120 hours

1200Z NAVGEM Model Run...

**For Tropical Storm Claudette…opens to a surface trough over 40N-70W at 18 hours

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives just north of the Azores by 114 hours….cyclonically loops at this location through 150 hours.