*******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.**********
...TUESDAY NOVEMBER 1 2022 4:12 AM EDT...
The Atlantic tropics are expected to remain active across the Caribbean region over the next week as follows:
(1) The central Caribbean disturbance has become Tropical Storm Lisa. Lisa is now en route to the Honduras/Belize coastal region... see Lisa section below for more information on expected impacts to land in this region.
(2) The south part of the current central US upper trough is forecast to move toward and then into the western Atlantic over the next four days. Meanwhile during the same four day timeframe... the current northeastern Pacific upper trough will develop a frontal system across North America whose warm sector amplifies an upper ridge over eastern North America... with this upper ridge causing the western Atlantic upper trough to evolve into a cut-off upper vortex that drifts south toward the Caribbean. A pair of disturbances could emerge as a result of this upper vortex in the 4 to 6 day window... one tropical in the central Caribbean supported by split flow upper divergence between the south side of the vortex and east side of the current northwestern Caribbean upper ridge cell... a second tropical or subtropical disturbance over the northeastern Caribbean Islands (from the Dominican Republic to the Virgin Islands) or western Atlantic waters just north of the islands to be supported by the eastern divergence zone of the vortex. No areas of interest are being declared for either potential future disturbance at this time as it is not clear if the two disturbanes could simply merge into a sprawling area of low surface pressure with no consolidated center... which would result in widespread rainfall instead of tropical cyclone development.
Elsewhere... the subtropical low pressure area that was previously near Bermuda has accelerated east-northeast into the open central Atlantic while quickly gaining organization and tropical characteristics in the last 24 hours. This system is again being monitored for signs of subtropical cyclone formation... see area of interest #42 section below for more information.
New to this site this year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development. In this scheme... will reset back to #1 at the start of next year (January 2023). The current area of interest in this blog post is designated #42 as the other numbers were used in previous birdseye view posts. This scheme is to reduce confusion as Atlantic tropical activity increases during the peak of the hurricane season... when multiple simultaneous areas of interest begin and end which previously required shuffling around the area of interest numbers from update to update.
TROPICAL STORM LISA... While passing south of Jamaica... the NHC upgraded the central Caribbean tropical low pressure spin to Tropical Storm Lisa as of 11 AM EDT Monday as it displayed a better defined swirl of clouds. Thunderstorm activity remained lopsided to the east of the swirl due to light westerly shear being imparted by lingering upper vorticity located just to the west. As of late the upper vorticity is in the process of dissipating while remaining cut-off from high-latitude cold air... which has allowed Lisa to build stronger thunderstorms that are also closer to the center of circulation. This has allowed the tropical storm to strengthen a little further 45 mph maximum sustained winds in recent hours.
Due to the western convergence zone of the upper trough tied to area of interest #42... surface ridging and associated steering easterly trade winds have recovered which has allowed Lisa to move increasingly faster toward the west. The current northwestern Caribbean upper ridge cell is expected to amplify northward due to warm air advection (northward warm air transport) ahead of a North American frontal system that will soon develop with the support of upper trough energy to move in from its current northeast Pacific position... the south side of this upper ridge cell is therefore expected to also contribute to Lisa's westward track as the tropical storm becomes stronger/taller and couples with the upper flow. Lisa is currently west-southwest of my previous forecast track and my updated one is adjusted accordingly. My forecast track remains on the southern side of the model spread and NHC official forecast as their are no expected mechanisms to pull Lisa north from its current latitude during the forecast period. This forecast strategy has performed well so far as the models and NHC official forecast have continued to shift southward while my forecast track has only required small adjusment. Also noting that the models still project a southward bend in the track forecast toward the latter part of the forecast period as surface ridging to the north gains strength under the western convergence zone of what will be a southern fracture of the current central US upper trough... as that fracture later pivots east across the southeastern US. The slight southward bend is incorporated into the forecast track shown below.
Regarding intensity... the opportunity for instensification will increase going forward as the lingering disruptive upper vorticity in Lisa's environment is dissipating as noted a couple of paragraphs up. Warm waters and low shear/outflow beneath the northwestern Caribbean upper ridge cell are the factors that will benefit Lisa. The tropical storm also appears to be relatively small in size and the models agree on the storm maintaining a compact structure... note small systems tends to have quick intensity changes both up and down as the pressure gradient between the center and outside of a small storm is greater relative to a larger storm undergoing a similar change in central pressure. In other words quick intensification is on the table. However I have lowered my intensity forecast and am now in agreement with the NHC by showing a category 1 peak intensity... as the updated forecast track shown below increases Lisa's land ineraction with Honduras in the 24 to 48 hour window. Although not shown explicitly in the intensity forecast below... it would not surprise me if Lisa becomes a slightly stronger category 1 hurricane between the 24 and 48 hour points... before its center slides inland by 48+ hours.
Due to Lisa being west-southwest of previous forecasts... the following changes have occurred regarding expected impacts to land areas:
(1) The tropical storm watches that were in effect for Jamaica and the Cayman Islands have been dropped.
(2) The northeastern corner of Nicaragua may see heavy rainfall with flash flooding potential from Lisa's south side by tonight.
(3) Tropical storm force winds with hurricane force gusts are possible along all of Honduras's northern coast due to the storm track being potentially parallel and near to the coast... with coastal surf accompanying these winds. Wind/surf impacts will now arrive sooner and by tonight along the northeast coast given the latest shift in the forecast track of Lisa... preparations here should be completed by no later than this afternoon. For the northwest coast of Honduras... preparations for wind/surf impacts should be completed by late tonight. Heavy rainfall with flash flood potential could spread across much of Honduras... sooner further east... and later further west.
(4) Tropical storm force winds... with hurricane force gusts... are possible along the Belize coast by late Wednesday should a further north track occur... with coastal surf accompanying these winds. Preparations here for possible wind and surf should be completed by Wednesday morning. Gusty winds and heavy rainfall with flash flood potential will spread inland in the more northern track scenario.
(5) Tropical storm force winds... with hurricane force gusts... are possible along the Caribbean coast of Guatemala by late Wednesday should a further south track occurr... with coastal surf accompanying these winds. Preparations here for possible wind and surf should be completed by Wednesday morning. Gusty winds will spread inland across central Guatemala should a more southern track occur... or spread inland over northern Guatemala from Belize should a more northern track occur. Heavy rainfall with flash flood potential could spread across much of Guatemala after Lisa makes landfall.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0600Z Nov 1)... 45 mph maximum sustained wind tropical storm centered well south-southwest of Jamaica at 15.8N-79.8W
IOH 24 Hr Forecast (0600Z Nov 2)... 65 mph maximum sustained wind tropical storm centered just offshore of northeastern Honduras at 15.8N-83.5W
IOH 48 Hr Forecast (0600Z Nov 3)... 75 mph maximum sustained wind hurricane centered just inland and over northwestern Honduras at 15.2N-87.5W
IOH 72 Hr Forecast (0600Z Nov 4)... Dissipating over Guatemala at 15N-90W
AREA OF INTEREST #42...The subtropical low pressure area that was previously near Bermuda... previously tagged as area of interest #42 in birdseye view post #143... has spent Halloween Monday resurrecting itself back from the dead as far as subtropical cyclone formation potential while continuing east-northeast into the open central Atlantic. Specifically the surface circulation has once again become less elongated and more circular... all while displaying an area of organized showers and thunderstorms near the center. Because this system and its thunderstorms is being supported by the divergence zone of the shortwave upper trough that has been incoming from the west... this system is essentially subtropical instead of fully tropical... and explains how this system has thunderstorm activity and some tropical character despite over water temps below 26 deg C. The NHC has re-introduced this system in earnest in their tropical weather outlook product... and already as of 2 AM EDT have assigned 50% odds of subtropical cyclone formation.
The divergence zone of the aforementioned shortwave upper trough has in addition to supporting this system also eroded the surface ridge to the north that was previously blocking the eastward progress of this circulation... thus the surface circulation has been allowed to accelerate east-northeast and better keep up with the upper westerly wind speed. In effect this has reduced the upper westerly shear which is how this system now has thunderstorm activity near its center. Although only half of the models in the computer model summary section below explicitly show subtropical cyclone formation... I have elected to go with greater than 50% odds (more likely than not) that subtropical cyclone formation occurs as the thunderstorm activity has recently grown stronger in nighttime infrared satellite pictures. My odds in the next 48 hours are in fact set in the 70 to 80% range as it would not surprise me at this point if this system is upgraded to a subtropical cyclone by the NHC later this morning. The peak odds are set at 48 hours as conditions could become even more conducive for subtropical development by that time despite this system accelerating northeastward into water temps in the low-20s of deg C as follows:
(1) The nearby shortwave upper trough is expected to merge with the current upper trough approaching from central Canada and north fracture of the current central US upper trough... with the merged upper trough becoming more amplified in response to amplified upper ridging that develops across eastern North America and northwest Atlantic (the amplifying upper ridging to be supported by the warm sector of a frontal system that will soon develop with the support of the current upper trough energy in the northeast Pacific). The more amplified and merged upper trough will produce increased supportive upper divergence on its east side and drop westerly shear levels further.
(2) The central Canada upper trough will bring colder upper air over this system (200 mb heights over this system dropping toward 1200 dekameters)... the increased instability produced by the cooling upper air temps combined with the increased upper divergence should be enough to support thunderstorm activity over the low-20 deg C water.
The rapid northeastward forecast track shown below is based on following the upper divergence maximum of the above-discusssed merged and amplifying upper trough from this past 1800Z GFS model run. Odds of subtropical development are sharply dropped to 0% by 72 hours as the rapid track vaults this system into much cooler water temps in the low-10s of deg C. Due to the significant amount of upper divergence anticipated on the east side of the upper trough... this system will liekly strengthen to hurricane-force despite losing tropical characteristics and become a concern for marine interests in the far northeast Atlantic.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Nov 2)... 70% chance of subtropical cyclone formation (central Atlantic near 36.5N-52W)
IOH 48 Hr Outlook (0600Z Nov 3)... 80% chance of subtropical cyclone formation (north Atlantic near 40N-46W)
IOH 72 Hr Outlook (0600Z Nov 4)... 0% chance of subtropical cyclone formation (northeast Atlantic near 54N-35W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 31) CMC Model Run...
**For Tropical Storm Lisa... makes landfall as a compact and stronger tropical storm over the southern coast of Belize at 60 hours... as an inland remnant low dissipates over northern Guatemala at 72 hours.
**For area of interest #42... becomes elongated and less tropical at 60 hours while continuing east-northeast to 38.5N-45W at 60 hours... current central Canada frontal cyclone moves into north Atlantic and absorbs this area of interest at 102 hours.
**South part of current central US upper trough evolves into cut-off upper vortex just northeast of the Bahamas by 96 hours... eastern divergence zone of upper vortex produces subtropical low near 24N-72.5W at 144 hours... subtropical low whirls westward in north side of upper vortex and moves into the central Bahamas by 162 hours.
1200Z (Oct 31) ECMWF Model Run...
**For Tropical Storm Lisa... makes landfall on north coast of Belize at 60 hours... as an inland remnant low dissipates over northern Guatemala at 78 hours.
**For area of interest #42... becomes elongated and less tropical at 66 hours while reaching 40.5N-44.5W... upper trough currently over central Canada moves into north Atlantic and transitions the remnant non-tropical low of this system into a frontal cyclone near 51.5N-37W at 84 hours... remnant frontal cyclone located in the far northeastern Atlantic near 56N-25.5W at 120 hours.
1800Z (Oct 31) GFS Model Run...
**For Tropical Storm Lisa... weakens to a remnant trough just offshore of northeastern Honduras at 27 hours... remnant trough dissiptes over Belize at 54 hours.
**For area of interest #42... becomes a subtropical cyclone near 35N-51.8W at 39 hours... subtropical cyclone strengthens near 39.2N-45.5W at 57 hours... transitions into a remnant frontal cyclone near 45.5N-35W at 72 hours... upper trough that approaches from its current position over central Canada produces a new frontal cyclone just northwest of the remnant frontal cyclone at 72+ hours with both frotnal cyclones orbiting each other through 90 hours with the duplex of cyclones reaching the vicinity of 55N-39W... through 99 hours the duplex of cyclones merge into one powerful cyclone located near 55.5N-34W... remnant cyclone shifts east to 55N-28.8W by 120 hours.
**North fracture of current central US upper trough moves into open central Atlantic by 75 hours while becoming more amplified due to amplifying eastern North America and northwest Atlantic upper ridge... eastern divergence zone of more amplified upper trough produces a subtropical low near 30N-52.5W at 96 hours... while generally stationary at this location evolves into a subtropical cyclone through 120 hours.
**South part of current central US upper trough evolves into cut-off upper vortex just northeast of the Bahamas by 96 hours due to amplifying eastern North America and northwest Atlantic upper ridge... eastern divergence zone of upper vortex produces subtropical low near 22.5N-66W at 156 hours
1800Z (Oct 31) NAVGEM Model Run...
**For Tropical Storm Lisa... makes landfall over the southern Belize coast at 60 hours... as an inland remnant low dissipates over the northern Guatemala/Mexico border at 78 hours.
**For area of interest #42... becomes a subtropical cyclone near 36.2N-48.W at 48 hours... subtropical cyclone strengthens near 40N-43W at 60 hours... transitions to remnant frontal cyclone near 49.8N-31.5W at 78 hours... remnant frontal cyclone located in far northeast Atlantic near 56.5N-25.5W at 120 hours