MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #69
*******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 23 2020 8:15 AM EDT...
See Tropical Storm Gonzalo and Tropical Depression Eight sections below for all active tropical cyclones being monitored in the Atlantic basin. Elsewhere...some long range computer models suggest that a tropical wave of low pressure to emerge from western Africa in the next 24 hours could develop in the open tropical Atlatnic Ocean next week. Should this tropical wave show signs of organization in the coming days...will consider adding it as another area of interest on this blog.
TROPICAL STORM GONZALO...Gonzalo's strengthening so far has been gradual instead of rapid as dry saharan air just to the north appears to be occasionally disrupting the thunderstorm activity in the circulation. Outside of the dry air...conditions are favorable for Gonzalo during the 120-hour forecast period as the tropical storm will remain below a cell of tropical upper ridging with low shear and upper outflow...the cell to be located between an upper vortex that has just become cut-off from the mid-latitude westerlies and will head southwestward around a northwest Atlantic upper ridge...and upper vorticity persisting in the western Atlantic and Caribbean Sea which will also be drifting westward. Gonzalo will also be moving over waters plenty warm for development...measuring at 28 to 29 deg C. Computer models remain split into two camps...one camp (GFS and NAVGEM) showing Gonzalo strengthening while producing thunderstorms that wall off the dry air and hitting the southern Lesser Antilles as a possibly strong tropical cyclone in three days...the other camp (CMC and ECMWF) showing Gonzalo weakening to a tropical wave as it crosses the islands. It is interesting to note that the models that show high strength initialize Gonzalo as a strong tropical storm...while the models that keep Gonzalo weak initalize Gonzalo as a small weak tropical low as Gonzalo is perhaps too small to be accurately represented in those lower-resolution models. The low-resolution NAVGEM intializes Gonzalo as a strong tropical storm but larger than it currently is...perhaps to get this low-resolution model to be more accurate regarding intial strength...so I think this makes this model may have a tendency to overdo the strength of Gonzalo with this strategy. The best initialization is the GFS which both captures the small size and current strength of the storm...and this run keeps Gonzalo at high strength while moving it into the southern Lesser Antilles and eastern Caribbean Sea.
The latest colorized infrared satellite shows a big gash in the thunderstorm activity which I believe is due to the dry air...so despite the GFS...for now I continue to put my intensity forecast in between the two camps of models and do not forecast hurricane strength at this time. But this is a difficult intensity forecast as Gonzalo could go either way. I then forecast weakening to begin once Gonzalo reaches the Caribbean Sea with the assumption the dry air will have been pushed moreso into Gonzalo by the large tropical wave to the east of the tropical storm. An increasing northward angle is shown in the forecast track in the Caribbean Sea with the assumption Gonzalo will be sufficiently strong/tall enough to be tugged by the upper vorticity currently in the Caribbean and western Atlatnic which is forecast to still be present...albeit at a further west position...by 120 hours. It should be noted this northward angle is higher in the GFS and NAVGEM models that keep Gonzalo very strong...as those models see Gonzalo as a very strong/tall system moreso tugged by upper southeasterly flow to the east of the upper vorticity...therefore if indeed Gonzalo stays stronger the forecast track may need some northward adjustment.
Due to the highly uncertain intensity forecast...interests in the southern Lesser Antilles should very closely monitor the progress of Gonzalo and begin making preparations for tropical storm...possibly hurricane conditions...to arrive on Saturday evening.
One final note about Gonzalo that I forgot to mention in yesterday's update while trying to catch up with the increasing activity in the Atlantic tropics...this is the earliest seventh named storm on record to form in the Atlantic basin...beating Tropical storm Gert which was named on July 24 2005. The hyperactive pace of the 2020 Atlantic Hurricane Season continues!
0 Hr Position (0600Z Jul 23)...65 mph maximum sustained wind tropical storm centered at 10N-47W
IOH 24 Hr Forecast (0600Z Jul 24)...65 mph maximum sustained wind tropical storm centered at 10N-52.5W
IOH 48 Hr Forecast (0600Z Jul 25)...65 mph maximum sustained wind tropical storm centered east-southeast of the Lesser Antilles at 10.4N-57.5W
IOH 72 Hr Forecast (0600Z Jul 26)...60 mph maximum sustained wind tropical storm centered in the southeastern Caribbean Sea just offshore of the Venezuela coast at 11.4N-62.5W
IOH 96 Hr Forecast (0600Z Jul 27)...50 mph maximum sustained wind tropical storm centered in the eastern Caribbean Sea at 13.4N-67.5W
IOH 120 Hr Forecast (0600Z Jul 28)...45 mph maximum sustained wind tropical storm centered in the central Caribbean Sea south of Haiti at 15.5N-72W
TROPICAL DEPRESSION EIGHT...The surface low pressure spin in the central Gulf of Mexico seeded by the north end of a tropical wave of low pressure has strenghtened into the eighth tropical depression of the 2020 Atlantic Hurricane Season. As the upper vorticity to the southwest that previously disrupted this system has continued to weaken...upper-level winds are becoming more favorable for development as upper anticyclonic flow with low shear and upper outflow extending from the southeatern United States upper ridge expands in the wake of the vorticity. In addition...the new tropical depression is well organized with a persistent circular area of thunderstorms at the center and banding features east of the central activity. However despite these observations and warm 30 deg C water...computer models refuse to strengthen this system before it makes landfall on the Texas coast tomorrow night/Saturday morning. Considering that maximum sustained winds are only 30 mph with a central pressure of 1009 mb (recently down to 1007 mb as of 8 AM EDT)...low enough to typically be at tropical storm strength...this tells me that the tropical depression is large and spread out in nature with a lax surface pressure gradient...which will require a lower than typical pressure to cause winds to rise. However given the healthy structure and favorable conditions...my intensity forecast is slightly higher than the National Hurricane Center's (NHC)...bringing max sustained winds to 50 mph instead of 45 mph shown by the NHC. I have adjusted my track forecast points south and eastward due to the current position and heading of the tropical depression. Steering is being provided by surface ridging over the eastern United States supported by the western convergence zone of a shortwave upper trough moving across eastern North America. I previously thought that after landfall this system would continue more norhward while rounding the west side of the ridge...but instead the models now show the depression continuing more west and less northward while drawn into a surface monsoonal low pressure field over Mexico. Therefore the southward adjustment in my forecast track is larger in the long range.
Unlike Tropical Storms Cristobal and Fay which made landfall in the United States when/where the COVID-19 virus outbreak was less severe...this system will be approaching coastal Texas at a time and location where a signficant COVID-19 emergency is ongoing. Given the more southward track...interests along the Texas coast from the Louisiana border all the way to Matagorda Bay and points just south of the bay...as well as areas just inland from this coastal region...should use today to gather supplies to manage impacts such as power outages or coastal storm surge...to avoid a last minute rush to potentially crowded stores in the event this well organized tropical depression strengthens briskly into a moderate or strong tropical storm in the favorable conditions that lie ahead for it. Avoiding crowds reduces the potential for contracting COVID-19. In the event you must retreive supplies in a crowded situation...frequent sanitizing of your hands and wearing a face mask will be necessary to protect you and those around you from COVID-19. Sanitize the packaging of purchased supplies before use in your residence. In the event you may have to leave due to a concern such as storm surge...consider planning the use of a family/friend residence further inland or a hotel location further inland in case you may need it..as a crowded public shelter may not as ideal for controlling your exposure to COVID-19. This system will be bringing impacts to the Texas coastal region by Friday (tomorrow) night.
0 Hr Position (0600Z Jul 23)...30 mph maximum sustained wind tropical depression centered in the Gulf of Mexico at 26N-90W
IOH 24 Hr Forecast (0600Z Jul 24)...50 mph maximum sustained wind tropical storm centered in the northwestern Gulf of Mexico at 27.5N-94W
IOH 48 Hr Forecast (0600Z Jul 25)...50 mph maximum sustained wind tropical storm centered at Matagorda Bay Texas at 28.5N-96W
IOH 72 Hr Forecast (0600Z Jul 26)...Remnant low pressure over southern Texas near 29N-99W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...For Tropical Storm Gonzalo...shown to cross the southern Lesser Antilles as a weak tropical or tropical low in 72 hours...weakens to a tropical wave in the southeastern Caribbean Sea shortly thereafter in 84 hours. For tropical depression eight...landfall as a tropical cyclone shown on Matagorda Bay Texas in 54 hours...continues westward inland across south Texas and into northeast Mexico where it loses its identity in 96 hours. Elsewhere...large tropical wave shown to emerge from western Africa in 24 hours...organizes into tropical low near 11.5N-47.5W in 144 hours...strengthens into possible tropical cyclone while moving into the central Lesser Antilles near 15N-60.5W in 198 hours.
0000Z ECMWF Model Run...For Tropical Storm Gonzalo...weakens to a tropical wave while crossing the southern Lesser Antilles in 72 hours (Gonzalo poorly represented at 0 hours while shown as a small weak low pressure instead of a compact tropical storm). For tropical depression eight...approaches landfall at southern Texas coast in 48 hours...loses its identity shortly theraefter. Elsewhere...large tropical wave shown to emerge from western Africa in 24 hours...organizes into tropical low near 12N-48W in 144 hours...strengthens into possible tropical cyclone while moving into the northern Lesser Antilles near 16N-61W in 192 hours.
0000Z GFS Model Run...For Tropical Storm Gonzalo...shown to cross the southern Lesser Antilles as a possibly strong compact tropical cyclone in 72 hours while centered near 14N-60.5W...makes landfall on the southern Haiti/Dominican Republic border in 120 hours still as a compact tropical cyclone. For tropical depression eight...shown approaching landfall near Matagorda Bay Texas in 42 hours...loses its identity shortly thereafter.
0000Z NAVGEM Model Run...For Tropical Storm Gonzalo...shows strengthening into a strong tropical cyclone...moves into the southern Lesser Antilles at high strength while passing near 13.5N-60.5W in 72 hours...passes just south of Puerto Rico in 102 hours...makes landfall on south coast of Dominican Republic at high strength in 114 hours. For tropical depression eight...shows landfall between Galveston Bay and Matagorda Bay on the Texas coast in 66 hours...loses its identity shortly thereafter.