*******Note that forecast 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.**********
...SUNDAY JANUARY 22 2023 6:23 PM EDT...
Computer model runs indicating the potential for a long-duration eastern-to-central Atlantic surface low pressure with possible tropical characteristics in 3+ days... therefore temporarily resuming daily birdseye view posts on this site. See area of interest #1 section below for more details.
As done on this site starting last year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development throughout the year... resetting back to #1 at the start of each year. This scheme is so that each area of interest retains a numeric identity from update to update... which reduces confusion when simultaneous areas of interest begin and end when tropical activity increases particularly during the Atlanitc Hurricane Season. I have not counted the short-lived northwest Atlantic tropical event on January 16 as #1 as that system was expected to quickly shed its tropical characteristics and not become identified as a subtropical or tropical cyclone by the National Hurricane Center... instead I am identifying the area of interest discussed below as #1 for this year (refer to special update #0A available on the home page of this site for a report on the January 16th event).
AREA OF INTEREST #1... A series of upper troughs are beginning to pivot across North America and around a polar cold core upper vortex that has settled over northeastern Canada within the last few days. Over the next few days... the eastern divergence zones of each North American upper trough is expected to produce a series of strengthening winter-time surface frontal cyclones that shift northeastward across the eastern United States... this pattern is beginning with the current broad frontal low over the eastern United States which in the next 24 hours is expected to strengthen into a frontal cyclone with the aid of its parent upper trough. Warm southerly flow ahead of each frontal cyclone is expected to in turn amplify the current western Caribbean warm core upper ridge across the western Atlantic... which in turn will cause upper troughs downstream of (northeast of) the upper ridge to amplify into eastern/central Atlantic cut-off upper vortices. The upper vortices are expected to become initially quasi-stationary while jammed between the amplifying western Atlantic upper ridge and current northeast Atlantic deep-layered ridge... over an area of low-20 deg C sea surface temperatures while the upper vortices themselves are forecast to be cold enough to produce instability and possible thunderstorms over these water temperatures (200 mb heights forecast to be well below 1200 dekameters... at around 1180 dekameters). Therefore the surface low pressure system to be initiated by the eastern divergence zones of the forming cut-off upper vortices could acquire tropical characteristics in the days ahead. The first of the upper vortices is expected to form from the current northwest Atlantic upper trough and its associated surface frontal cyclone and cold front. Therefore for this update this area of interest for possible tropical development is being initiated along the aforementioned cold front.
The forecast track in the outlook below and for the first 48 hours is based on the position of the eastern divergence zone of the cut-off upper vortex to form from the current northwest Atlantic upper trough. This divergence zone is expected to kick off an eastern Atlantic surface low pressure area along the cold front mentioned in the prior paragraph... which by 72 hours is projected to whirl beneath the upper vortex as a typical post-mature frontal low. It is also during this time the current central North America upper trough will be upstream of (northeast of) the amplifying western Atlantic upper ridge and become a potential second cut-off upper vortex incoming from the northwest... therefore the 72 hour position in the outlook below places the surface low in the northwest quadrant of the initial upper vortex and toward the supportive southeastern divergence zone of the incoming second one. By 96+ hours the two upper vortices are likely to merge while the western Atlantic and northeast Atlantic ridges also merge to the north.... resulting in a west-southwest track of the surface low in the steering flow on the south side of the merged ridge. Because the upper layer of the steering merged deep-layer ridge will tend to be southwest of the surface layer... the upper vortex is expected to stay to the east while the surface low moves faster to the west... eventually placing the surface low on the northwest quadrant of the upper vortex. At this position the upper vortex will also aid in the south angle of the surface low's track while upper convergence in this quadrant of the vortex causes a long-range (120+ hour) weakening trend of the surface low.
I assign a peak 10% odds of subtropical cyclone formation beginning at 72 hours when the surface low pressure area becomes stacked with the forecast initial cut-off upper vortex... with the two combining to make deep-layer cyclonic flow low in wind shear while the instability provided by the cold temps of the upper vortex aids in thunderstorm generation... conditions potentially conducive for the surface low to acquire tropical characteristics (tropical meaning the surface low pressure becomes aided by the warm core outflow generated by thunderstorm latent heat release). The low odds are a reflection of ongoing mixed results in model runs... specifically there is some disagreement in the middle of the 5-day forecast period regarding the amount of seperation between the current incoming central North American upper trough and initial eastern/central Atlantic upper vortex. For example the 0000Z ECMWF run in the computer model summary below suggests more upper ridging/seperation between the two... allowing for the upper vortex to have a more focused eastern divergence zone that seeds a well-defined surface low pressure center needed for subtropical cyclone formation. Whereas the 1200Z GFS model run suggested less seperation... resulting in a broader surface low pressure area with possible multiple centers due to the competing influences of the divergence zones of the incoming upper trough and initial upper vortex. It is interesting to note the 12Z GFS suggests that the divergence zone of the incoming upper trough/second upper vortex may help the broad surface low develop a better-defined center but simply later than when the 0000Z ECMWF showed... whereas other solutions with the broad surface low never show the formation of a well-defined center. Odds of subtropical development in future updates will be adjusted as needed pending later computer model data and/or observations.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jan 23)... 0% chance of subtropical cyclone formation (eastern Atlantic near 35N-36W)
IOH 48 Hr Outlook (1800Z Jan 24)... 0% chance of subtropical cyclone formation (eastern Atlantic near 32.5N-35W)
IOH 72 Hr Outlook (1800Z Jan 25)... 10% chance of subtropical cyclone formation (eastern Atlantic near 31N-35W)
IOH 96 Hr Outlook (1800Z Jan 26)... 10% chance of subtropical cyclone formation (central Atlantic near 31N-40W)
IOH 120 Hr Outlook (1800Z Jan 27)... 10% chance of subtropical cyclone formation (central Atlantic near 29N-44W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Jan 22) CMC Model Run...
**For area of interest #1... north-south elongated frontal low becomes defined near 40N-38W at 18 hours... through 42 hours frontal low dives south-southeast while developing a southern center near 28N-35W... through 84 hours frontal low evolves into a more circular but broad subtropical low near 25.5N-34.5W... broad subtropical low swings west and weakens through 120 hours while reaching 25N-45W
0000Z (Jan 22) ECMWF Model Run...
**For area of interest #1... north-south elongated frontal low becomes defined near 41.5N-36W at 36 hours... through 54 hours frontal low dives south while developing a southern center near 31.5N-34W... through 72 hours frontal low develops into a potential subtropical cyclone while moving south-southwest to 26N-38W... subtropical cyclone weakens to a broad subtropical low while swinging southeast to 23N-34.5W through 102 hours... broad subtropical low swings west and weakens through 120 hours while reaching 24.5N-40W
1200Z (Jan 22) GFS Model Run...
**For area of interest #1... north-south elongated frontal low becomes defined near 39N-38.8W at 18 hours... through 39 hours frontal low dives south-southeast while developing a southern center near 31.5N-34.5W... through 72 hours frontal low evolves into a more circular but broad subtropical low near 29N-34.5W... through 93 hours broad subtropical low swings west and strengthens while reaching 29.8N-39.5W... through 120 hours broad subtropical low drifts southwest to 25N-42W while beginning to gradually weaken.
1200Z (Jan 22) NAVGEM Model Run...
**For area of interest #1... north-south elongated frontal low becomes defined near 41N-42.5W at 18 hours... through 36 hours frontal low dives south-southeast while developing a southern center near 33N-34W... through 78 hours frontal low evolves into a more circular but broad subtropical low while moving further south to 23.5N-34W... through 120 hours broad subtropical low accelerates west to 24.5N-46W while weakening.