MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #51
Updated: Jul 17, 2021
*******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 JULY 15 2021 11:37 PM EDT...
See area of interest #1 section below for an update on the potential for tropical development in northwest Atlantic midway between Bermuda and Newfoundland.
Elsewhere…tropical development in the Atlantic basin has been suppressed by low-latitude (southern located) upper vorticity toward the west side of the basin and dry Saharan air toward the east side of the basin. However some recent model runs suggest in about five days a strong tropical wave of low pressure from Western Africa will emerge into the eastern tropical Atlantic. The current configuration of the Madden Julian Oscillation (MJO) has favored suppressed thunderstorm activity in the Atlantic tropics since July started (https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml). While the recent upheaval of activity in the eastern Pacific suggests the favorable phase of the MJO might finally be shifting back east toward the Atlantic…the favorable MJO pulse may not make it east all the way to the forecast tropical wave…and none of today’s model runs develop the wave after it enters the Atlantic…perhaps as the wave is also forecast to exit Africa a little further to the north where it may ingest dry Saharan air. Therefore for now… I have not declared a new area of interest for the forecast tropical wave.
AREA OF INTEREST #1…Recent colorized infrared satellite images of the surface low pressure in the northwest Atlantic…from tropicaltidbits.com…left taken at 2105Z…right taken at 0155Z. Red plus marks the surface center tracked by the National Hurricane Center (NHC). Yellow plusses mark smaller vortices that have recently become apparent:
Over the last 24 hours…the surface low pressure spin in the open northwest Atlantic has seen its primary surface swirl lose its definition while at the same time showers and thunderstorms have increased on the southeast side of the circulation while aided by the outflow of a sprawling upper ridge axis in the region. Meanwhile the thunderstorm activity on the northwest side of the circulation of has been impeded by light northwesterly shear as the surface low has been east of the upper ridge axis rather than directly below it…which has been especially made true by the fact the surface low has failed to move west past 60W longitude. This maybe due to the drag of the Atlantic surface ridge to the south which may have impeded the steering influence of the northwest Atlantic surface ridge to the north. Recently however…the surface low has begun to drift north under the influence of the northwest Atlantic surface ridge’s west side…and it could be the increase in showers and thunderstorms over the last day is due to this system reaching the northeast end of the warm Gulf Stream as the latest sea surface temperature analysis shows some 26 deg C water sticking out a little past 60W longitude and into the path of the recent north track. The NHC has suggested the center of the surface low has moved north from 37.5N-59W at 1800Z to 38N-59W as of late. This system is showing disorganization recently as seen in the above sample of satellite pictures…with two smaller vortices popping up to the west and east of the NHC suggested center instead of this system having a single surface vortex. The smaller vortex to the east is currently the most defined…seen sliding northward from a thunderstorm burst that was present a few hours ago as if that burst helped to spawn it.
In my updated outlook below…my forecast track is nudged east due to the current position of the surface low. As the surface low continues north…it will head toward cooler waters in the next 24 hours. However in the midst of the cooler water…the latest sea surface temperature analysis shows a new small spot of warm 26 deg C water near 41N-58W. In addition an upper trough currently entering the Atlantic from eastern Canada and also heading toward this system…but the cool core upper trough is weakening into small vortices due to warming southerly flow on the west side of the steering northwest Atlantic surface ridge. If the divergence zone of one these small upper vortices lines up with the eastern well-defined surface vortex mentioned in the prior paragraph…perhaps the surface vortex could get enhanced by the upper divergence and warm water spot at 41N-58W (https://www.nhc.noaa.gov/sst/rsst_atl_loop.php). The upper divergence zone of the small upper vortex could be why some of the recent model runs showed the surface low pressure lasting longer compared to yesterday’s runs. For tropical development to occur in the next 24 hours however… we are basically talking about the perfect alignment between a surface vortex…assuming the vortex lasts…and a small upper vortex and warm water spot. Therefore I have chosen to lower odds of tropical development to 0%…and plan this to be my final statement on this system on this blog unless the above-mentioned perfect alignment scenario does in fact happen…or unless the NHC is still mentioning this system in their tropical weather outlook by my next update.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Jul 17)…0% chance of tropical cyclone formation (northwest Atlantic near 42N-58W)
...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 area of interest #1...surface low turns north and weakens to a surface trough near 43.5N-55W at 42 hours.
1200Z ECMWF Model Run...
**For area of interest #1…surface low turns north and weakens to a surface trough near 42.5N-53.5W at 48 hours.
**Large and strong tropical wave forecast to emerge from Western Africa to the northeast of the Republic of Cabo Verde Islands at 120 hours…wave loses low pressure spin at 168 hours near 34W longitude.
1200Z GFS Model Run...
**For area of interest #1...surface low turns north and weakens to a surface trough near 41N-57.5W at 36 hours.
**Large and strong tropical wave forecast to emerge from Western Africa at 120 hours…surface low pressure spin of tropical wave centered at 11N-52.5W at 165 hours.
1200Z NAVGEM Model Run...
**For area of interest #1...surface low turns north and weakens to a surface trough near 41.2N-56.5W at 36 hours.
**Large and strong tropical wave forecast to emerge from Western Africa at 120 hours…large pressure spin of the wave located just southwest of the Republic of Cabo Verde Islands at 168 hours.