*******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.**********
...THURSDAY JULY 20 2023 12:55 PM EDT...
Tropical Storm Don is expected to continue westward and then northwestward across the open central and northwestern Atlantic over the next few days while potentially strengthening... see Don section below for more information. Elsewhere... see area of interest #14 section below for an update on the current eastern Atlantic tropical disturbance and area of inerest #15 section below for an update on the surface low pressure area in the northwestern Atlantic.
TROPICAL STORM DON... Colorized infrared satellite image of Tropical Storm Don while it obtained 50 mph maximum sustained winds earlier today... image taken at 0620Z:
Don continues to wander around in the open central Atlantic. Overnight the tropical storm's core of thunderstorm activity continued to expand in size and intensity while it took advantage of an area of split flow upper divergence between the back (west) side of the current northeast Atlantic upper trough and front (southeast) side of the northwest Atlantic deep-layer ridge. As a result the tropical storm reached a peak of 50 mph maximum sustained winds. The thunderstorm acivity has since taken a marked downward decline as the tropical storm has moved westward and away from the split flow upper divergence and into neutral (no divergence or convergence) upper flow on the north side of a cut-off upper vortex recently left behind by the northeast Atalntic trough and south side of the deep-layer ridge. Therefore for the short-term I forecast Don to weaken back to a minimal tropical storm in the less conducive upper air environment. 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 nudged northward due to Don's current position relative to the previous forecast. By 36 hours the forecast track puts Don in supportive split flow upper divergence between the north side of the cut-off upper vortex and southwest side of the deep-layer ridge... and by 48 hours Don is forecast to be near or over 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. Thus I forecast Don to acheive peak strength during this timeframe. To finish off the forecast... I project Don to gradually weaken in the low shear environment and also lose tropical characteristics by 96 hours as Don moves northeastward across markedly cooler waters east of Newfoundland. If Don retains sufficient strength as it passes by Newfoundland... surf induced by its circulation could reach the eastern shores of Newfoundland in about 3 days.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jul 20)... 50 mph maximum sustained wind tropical storm centered at 34.1N-41.6W
IOH 24 Hr Forecast (1200Z Jul 21)... 40 mph maximum sustained wind tropical storm centered at 35.5N-46W
IOH 48 Hr Forecast (1200Z Jul 22)... 60 mph maximum sustained wind tropical storm centered at 38.5N-50.5W
IOH 72 Hr Forecast (1200Z Jul 23)... 50 mph maximmum sustained wind tropical storm losing tropical characteristics while centered at 43N-51W
IOH 96 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***************************
Peak Strength (0000Z Jul 21)... 60 mph maximum sustained wind tropical storm centered at 34.9N-43.8W
Loss of tropical cyclone status (1200Z Jul 24)... 35 mph maximum sustained wind non-tropical remnant low centered in the north Atlantic at 46.7N-46.1W
AREA OF INTEREST #14... In the eastern tropical Atlantic... a tropical disturbance persists while consisting of an east-west elongated region of showers and thunderstorms around 10N latitude supported by the outflow of a tropical upper ridge in the region. Albeit the activity has become anemic over the last several hours due to dry Saharan air lurking to the north. The current NHC surface analysis shows a tropical wave of low pressure passing through the area around 30W longitude... and 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 wave is embedded in an elongated envelope of low-level low pressure/spin that has been induced by the aforementioned elongated region of thunderstorms and upper outflow. Satellite animation and the CIMSS 850 mb vorticity product also shows a better defined spin is also present to the west of the tropical wave and toward 40W longitude. The computer model summary below shows that some recent models runs are now favoring the circulation toward 40W instead of the tropical wave... for example the CMC and ECMWF. Meanwhile the GFS has the tropical wave merge with the circulation at 40W... with the merger then continuing westward across the tropical belt of the Atlantic. Noting that none of these mentioned models develop this disturbance beyond a tropical low.
Regarding forecast track... the elongated envelope of low pressure and tropical wave are only moving slowly westward due to the surface ridge weakness caused by Tropical Storm Don. Once the tropical storm accelerates northwestward and away and the surface layer of the current northwest Atlantic deep-layer ridge approaches the westward speed of this disturbance is expected to increase in 48+ hours. Through day 5 the northern outflow of the 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 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 also adjusted the forecast track points westward as the tropical wave is further west of my previous forecast. Regarding odds of tropical cyclone formation... I agree with the NHC in showing low odds due to the negative factors of the dry Saharan air... the tropical wave being in competition with an elongated low pressure envelope instead of having a consolidated surface low pressure area... and lackluster computer model support. The only positive is the current central Atlantic cut-off upper vortex is expected to retrograde wesward and away around the aforementioned deep-layer ridge which will allow the tropical upper ridge to expand and hence provide a larger area of low wind shear and upper outflow. I wait till 72+ hours to show non-zero odds of tropical cyclone formation which is when the tropical wave is most likely to have caught up to and merged with the circulation at 40W... giving a higher chance for a consolidated circulation needed for development. I have also lowered my peak odds of tropical cyclone formation to 10% in this update given the current anemic shower and thunderstorm pattern.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jul 21)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-32.5W)
IOH 48 Hr Outlook (1200Z Jul 22)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-36W)
IOH 72 Hr Outlook (1200Z Jul 23)... 5% chance of tropical cyclone formation (central tropical Atlantic near 11N-41W)
IOH 96 Hr Outlook (1200Z Jul 24)... 10% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-46W)
IOH 120 Hr Outlook (1200Z Jul 25)... 10% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-51W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************
Formation chance through 48 hours...0%
Formation chance through 7 days (168 hours)...20%
AREA OF INTEREST #15... The elongated surface low pressure area in the northwestern Atlantic has consolidated further north over cooler waters. Therefore as it continues northeastward into Newfoundland over the next 24 hours (while steered by the west side of the current northwest Atlantic deep-layer ridge)... tropical cyclone formation will not be possible. This is my final statement on this area of interest on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jul 21)... 0% chance of tropical cyclone formation (northeastern Newfoundland near 48N-55W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*****************************
Not in the official outlook
...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 20) CMC Model Run...
**For Tropical Storm Don... curves west and then northwest to 40N-50W through 72 hours while maintaining strength... continues north and then northeast into cooler north-central Atlantic waters through 126 hours where it weakens to a remnant trough near 46.5N-41.5W
**For area of interest #14... no development shown
**For area of interest #15... surface low dissipates after making landfall on south-central Newfoundland at 30 hours.
**To the west of AOI#14... a tropical low becomes better defined near 11.5N-38W at 24 hours... accelerates west and reaches 14.5N-56W at 120 hours
0000Z (Jul 20) ECMWF Model Run...
**For Tropical Storm Don... curves west and then northwest to 40N-50W through 72 hours while gradually weakening... continues north and then northeast into cooler waters where it weakens to a remnant trough near 47N-48W at 108 hours
**For area of interest #14... no development shown
**For area of interest #15... surface low dissipates after making landfall on south-central Newfoundland at 30 hours.
**To the west of AOI#14... a tropical low becomes better defined near 11.5N-38.5W at 18 hours... accelerates west and weakens to a tropical wave while crossing 53W longitude
0600Z (Jul 20) GFS Model Run...
**For Tropical Storm Don... curves west and then northwest to 40N-51W through 60 hours while maintaining strength... passes just southeast of Newfoundland through 90 hours as a compact tropical storm gradually losing strength and tropical characteristics over cooler waters... accelerates east-northeast to 50N-44W through 108 hours where it weakens further to a remnant trough.
**For area of interest #14... through 78 hours tropical wave currently near 30W longitude merges with tropical low to the west near 10N-40W... the merger continues westward as a tropical low that reaches 11N-50W at 120 hours.
**For area of interest #15... makes landfall over south-central Newfoundland at 21 hours and dissipates while reaching the northeast coast of Newfoundland at 30 hours
0600Z (Jul 20) NAVGEM Model Run...
**For Tropical Storm Don... curves west and then northwest to 39N-50W through 54 hours while gradually weakening... while continuing north-northeast weakens further to a trough while reaching 51N-45W at 96 hours
**For area of interest #14... no development shown
**For area of interest #15... no development shown
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