MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #36
Updated: Jul 23
*******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.**********
...FRIDAY JULY 21 2023 12:13 PM EDT...
Tropical Storm Don is expected to continue northwestward into waters offshore of eastern Newfoundland... arriving there by Sunday and into Monday. See Don section below for more information on the tropical storm. Elsewhere... see area of interest #14 section below for an update on the current eastern Atlantic tropical disturbance now moving into the central tropical Atlantic. Interests in the southern Lesser Antilles should be aware of this disturbance as it is expected to move into the islands by Wednesday and there is an increasing chance of tropical cyclone formation.
TROPICAL STORM DON... After a few days of wandering in the open central Atlantic... Tropical Storm Don is finally in the process of exiting the region and accelerating toward the northwestern Atlantic. The tropical storm has maintained 50 mph maximum sustained winds while redeveloping a small ring of showers and thunderstorms around its center. In the above birdseye view charts the 200 mb upper layer of the atmosphere is neutral (no divergence or convergence) as Don continues westward in linear deep-layer easterly flow around the north side of an upper vortex and south side of the passing north Atlantic deep-layer ridge. Its possible then that Don has developed a layer of warm core outflow below the 200 mb layer which is helping the tropical storm... and the latent heat release of the current shower and thunderstorm ring will only help Don in keeping its warm core outflow layer. The deep-layer ridge will continue slowly eastward as a typical mid-latitude amplified feature... and the forecast track for Don shows a curve toward the northwest and then northeastward as Don later rounds the west side of the passing deep-layer ridge. My updated track below is unchanged as the previous forecast has performed quiet well so far. Over the next 24 hours the forecast track brings Don over/near more favorable 26 deg C waters and underneath the western side of the deep-layer ridge where low shear and upper outflow may help Don further in a tropical manner. And given Don's already healthy structure as indicated by the ring-like cloud pattern and slightly higher initial intensity than I previously forecasted... I have slighlty raised my peak intensity forecast for Don. To finish off the forecast... I project Don to gradually weaken in the low shear environment and also lose tropical characteristics by 72 hours as Don moves northeastward across markedly cooler waters east of Newfoundland. Don has a chance to bring coastal surf to the eastern shores of Newfoundland Sunday and into Monday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jul 21)... 50 mph maximum sustained wind tropical storm centered at 35.4N-45.6W
IOH 24 Hr Forecast (1200Z Jul 22)... 65 mph maximum sustained wind tropical storm centered at 38.5N-50.5W
IOH 48 Hr Forecast (1200Z Jul 23)... 50 mph maximmum sustained wind tropical storm losing tropical characteristics while centered at 43N-51W
IOH 72 Hr Forecast (1200Z Jul 24)... Remnant low centered east of Newfoundland at 47N-49W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Loss of tropical cyclone status (0000Z Jul 24)... 40 mph maximum sustained wind non-tropical remnant cyclone centered east-southeast of Newfoundland at 46.1N-49.1W
AREA OF INTEREST #14... In the eastern tropical Atlantic... a tropical disturbance has been present consisting of an east-west elongated surface low pressure envelope with an embedded tropical wave of low pressure... of African origin... passing through. The disturbance has been supported by an elongated region of upper outflow induced by a tropical upper ridge in the region. The elements of the disturbance have been moving slowly as steering remains weak thanks to the surface ridge weakness caused by Tropical Storm Don. As of 0600Z the NHC TAFB surface analysis indicated the tropical wave had drifted westward to 32.5W longitude... however the more recent 1200Z analysis showed the wave had retrograded eastward back to 30W longitude. This retrograding could be due to the tug of an additional tropical wave that has recently emerged from western Africa. Meanwhile the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) shows that the elongated surface low pressure envelope has consolidated toward the west... near 11N-39W... around a better defined spin that has been gradually developing to the west of the tropical waves. In fact this better defined spin has recently developed a small core of organizing thunderstorm activity and has become the focus of this disturbance.
Regarding forecast track... this disturbance is forecast to increasingly accelerate westward as Tropical Storm Don moves northwestward and away and as the steering surface layer of the current north Atlantic deep-layer ridge approaches. Through day 5 the northern outflow of the regional tropical upper ridge is expected to converge with the southern outflow of the mid-latitude deep-layer ridge... resulting in a strengthening and expansion of the steering surface layer of the deep-layer ridge. This should result in a largely westward heading with little northward angle during the forecast period. I have once again had to adjust the forecast track points westward as the focus of this disturbance is now associated with the developing tropical low pressure circulation near 11N-39W. Regarding odds of tropical cyclone formation... I agree with the NHC in notably raising odds of development due to the formation of an organizing thunderstorm core with our tropical low pressure circulation. Another positive for this disturbance includes the westward retrogression of the current central Alantic upper vortex around the mid-latitude deep-layer ridge... which is allowing the regional tropical upper ridge and its supporting low shear and upper outflow to expand. Negatives going against this disturbance include dry Saharan air lurking to the north... ongoing lackluster computer model support... and for the long-term a wall of western Atlantic warm core upper ridging expected to persist as upper vorticity will remain trapped over eastern North America and produced more surface frontal systems that will transport warm air northward across the western Atlantic. The western Atlantic wall of upper ridging may push a portion of the suppressing central Atlantic upper vortex southwestward into the Caribbean and into the long-range track of this disturbance as it later crosses the Lesser Antilles and heads into the Caribbean. While weighing the postives and negatives I assign a peak of 50% odds of tropical cyclone formation in my updated outlook below. Note the model runs in the model summary section below were ran before 1200Z... before the development of the organizing thunderstorm core. Therefore model runs later today may become more bullish on development as this system heads toward the Lesser Antilles within the next five days... which may warrant even higher odds of tropical cyclone formation in future updates.
Interests in the southern Lesser Antilles should be aware of this system as it could bring impacts (gusty winds... heavy rains... and coastal surf) by Wednesday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jul 22)... 20% chance of tropical cyclone formation (central tropical Atlantic near 11N-41W)
IOH 48 Hr Outlook (1200Z Jul 23)... 40% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-45W)
IOH 72 Hr Outlook (1200Z Jul 24)... 50% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-50W)
IOH 96 Hr Outlook (1200Z Jul 25)... 50% chance of tropical cyclone formation (east of the southern Lesser Antilles at 12N-55W)
IOH 120 Hr Outlook (1200Z Jul 26)... 50% chance of tropical cyclone formation (vicinity of Barbardos near 12.5N-60W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************
Formation chance through 48 hours...20%
Formation chance through 7 days (168 hours)...40%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/). Due to ongoing outage of ECMWF model data at Florida State University site... used Tropical Tidbits (https://www.tropicaltidbits.com/analysis/models/) for ECMWF model.
0000Z (Jul 21) CMC Model Run...
**For Tropical Storm Don... curves northwest to 39.5N-50W through 42 hours while maintaining strength... continues north and then northeast into cooler north-central Atlantic waters through 90 hours where it weakens to a remnant trough near 49N-44W
**For area of interest #14... no development shown
0000Z (Jul 21) ECMWF Model Run...
**For Tropical Storm Don... curves northwest to 40N-51W through 42 hours while gradually weakening... continues north and then northeast into cooler waters where it weakens to a remnant trough near 48.5N-48W at 78 hours
**For area of interest #14... tropical low currently near 11N-39W becomes the dominant feature and later accelertes west... weakens to a tropical wave while crossing 46W longitude at 72 hours
**Additional tropical wave to emerge from west coast of Africa develops into a tropical low southwest of the Republic of Cabo Verde Islands at 102 hours... tropical low reaches 14N-41W by 168 hours.
0600Z (Jul 21) GFS Model Run...
**For Tropical Storm Don... curves northwest to 40N-51W through 36 hours while maintaining strength... passes just southeast of Newfoundland through 63 hours as a compact tropical storm gradually losing strength and tropical characteristics over cooler waters... accelerates east-northeast to 49N-45W through 81 hours where it weakens further to a remnant trough.
**For area of interest #14... no development shown
0600Z (Jul 21) NAVGEM Model Run...
**For Tropical Storm Don... curves northwest to 39.5N-49W through 30 hours while gradually weakening... while continuing north-northeast weakens further to a trough while passing just east-southeast of Newfoundland at 60 hours
**For area of interest #14... tropical low currently near 11N-39W becomes the dominant feature and later accelertes west... weakens to a tropical wave while crossing 46W longitude at 66 hours