*******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.**********
...MONDAY NOVEMBER 1 2021 2:08 AM EDT...
Satellite image as of 2330Z (Oct 31). Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green are in the NHC 2-day tropical weather outlook:
NHC TAFB Surface Analysis 1200Z (Oct 31):
GFS Model Upper-Level Winds 1200Z (Oct 31):
The Atlantic tropics are expected to remain active over the next 48 hours… after which time Subtropical Storm Wanda in the open central Atlantic will likely lose tropical characteristics and all current areas of interest are likely to diminish. See Wanda and area of interest sections below for more information.
SUBTROPICAL STORM WANDA…Wanda’s parent upper vortex has continued southeast in the flow between the northwest Atlantic upper ridge and northeast Atlantic upper trough. However that has not directly translated into a southeast motion for Wanda as the subtropical Storm has been on the southwest side of the upper vortex… and as a result has largely spent the last 24 hours moving due east under the steering influence of that quadrant of the upper vortex. Now that Wanda has aligned with the upper vortex… models have come into agreement that Wanda will spend the next 24 hours undergoing a cyclonic loop beneath the vortex… and this has already started with Wanda turning on a southwest drift (the cyclonic loop will result in a southwest motion… followed by south… east… then a northeast motion). My updated forecast track below is adjusted north based on Wanda’s recent more east and less south track… and also is adjusted to account for the cyclonic loop expected in the next 24 hours.
By 24 hours… the northwest Atlantic upper ridge will be making its way into the northeastern Atlantic. The eastern convergence zone of this upper ridge and adjacent eastern Atlantic upper ridge is expected to produce strong surface ridges to the east that will block eastward progress of Wanda. At the same time... the current northeast US to west Atlantic upper trough will be approaching from the west… with the flow between the upper trough and surface ridges turning Wanda north. Because this upper trough is likely to approach in an amplified state...it has potential to increase the upper divergence over Wanda and keep shear levels low. However the upper trough is not forecast to be cold enough for thunderstorm generation and tropical development… and in fact is forecast to be warmer than the current overhead upper vortex. Therefore by 48 hours I anticipate Wanda to lose tropical characteristics… however while maintaining strength from the eastern divergence zone of the upper trough. The intensity forecast below also no longer shows strengthening or acquisition of fully tropical characteristics as the overhead upper vortex has warmed to above 1200 dekameters in height at 200 mb… reducing the instability needed for thunderstorms. This is evidenced by the loss of Wanda’s solid thunderstorm canopy… which has instead become replaced by weaker and broken thunderstorm bands. My prior forecast assumed the previous thunderstorm canopy might strengthen Wanda slightly and allow it develop a fully tropical warm core… but this did not pan out as the canopy quickly faded after the prior forecast.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Nov 1)… 50 mph maximum sustained wind subtropical storm centered at 35.6N-44.1W
IOH 24 Hr Forecast (0000Z Nov 2)… 50 mph maximum sustained wind subtropical storm centered at 33N-41W
IOH 48 Hr Forecast (0000Z Nov 3)…50 mph maximum sustained wind non-tropical remnant cyclone centered at 37.5N-40W
AREA OF INTEREST #1… The upper trough moving into the western Atlantic from the northeastern United States has driven a cold front into the southern Caribbean Sea. Based on the latest satellite imagery… the tail end of the front appears to be evolving into a tropical low pressure spin near 12N-81W featuring curved bands of thunderstorms on its southwest side. The tropical low pressure is being aided by the outflow of an ongoing upper ridge in the western Caribbean. The upper flow is also split between the south side of this upper ridge and south side of upper vorticity located in the eastern Caribbean… with the split flow upper divergence also aiding this emerging tropical low. This tropical low has little time over water as a surface ridge building over North America will begin to steer it west into Nicaragua and Costa Rica. However given the appearance of thunderstorm bands… I have assigned low 10% odds of tropical cyclone formation before it makes landfall. Regardless of further development or not… heavy rains are possible over Nicaragua and Costa Rica over the next day or so.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Nov 2)… 10% chance of tropical cyclone formation (just offshore of the southern Nicaragua coast near 12N-83W)
IOH 48 Hr Outlook (0000Z Nov 3)… 0% chance of tropical cyclone formation (southwestern Nicaragua near 12N-86W)
AREA OF INTEREST #2… The tropical low pressure in the eastern tropical Atlantic continues to be guided more north in its westward track by the adjacent spin to the west recently left behind by the tropical wave at 35W longitude. As such… the center of the tropical low passed 12.5N-29.5W at 0000Z… and my updated forecast track shown below is nudged north over the previous. The tropical low pressure is also heading northwest toward the surface ridge weakness associated with Subtropical Storm Wanda. The tropical low pressure has been protected from shear via the amplifying east end of the warm tropical upper ridge in the region… with the amplification supported by warm southerly flow occurring on the east side of Wanda. As of late… the tropical low is beginning to exit the upper ridging and is entering a belt of southwesterly shearing upper winds being generated by the upper vortex over Wanda. However the tropical low is still producing organized bands of thunderstorm activity on its east side… and so I still assign 30% odds of development in the next 24 hours. Note this is lower than the peak 50% odds I assigned yesterday when the tropical low was fully embedded below the low shear of the tropical upper ridge. Once the tropical low becomes fully embedded in the shearing upper winds by 48 hours… I drop development odds to 0%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Nov 2)… 30% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-33W)
IOH 48 Hr Outlook (0000Z Nov 3)… 0% chance of tropical cyclone formation (eastern tropical Atlantic near 19N-36W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run...
**For Subtropical Storm Wanda… undergoes a cyclonic loop over the next 48 hours… afterwards accelerates northeast and reaches 48N-30.5W at 120 hours as a remnant non-tropical frontal low.
**For area of interest #1…tropical low becomes defined at 10.5N-80.5W at 30 hours… makes landfall in northern Costa Rica at 54 hours
**For area of interest #2… surface low reaches 31.5N-52.5W at 120 hours
1200Z ECMWF Model Run...
** For Subtropical Storm Wanda…undergoes a cyclonic loop over the next 48 hours… afterwards accelerates northeast and reaches 40N-36W at 120 hours as a potentially stronger subtropical storm
**For area of interest #1…tropical low becomes defined at 12N-80.5W at 24 hours… makes landfall near the Costa Rica/Nicaragua border just after 48 hours
**For area of interest #2… no development shown
1800Z GFS Model Run...
** For Subtropical Storm Wanda…undergoes a cyclonic loop over the next 48 hours… afterwards accelerates northeast and reaches 42N-31W at 120 hours as a potentially stronger subtropical storm
**For area of interest #1…tropical low becomes defined at 11.5N-79.5W at 9 hours… tropical low pressure gradually loses defintion at 24 hours and no development forecast
**For area of interest #2… no development shown
**Currently developing North America upper vortex begins to shift offshore as an upper trough by 96+ hours… eastern divergence zone of trough supports a compact surface low with tropical character near 36.5N-67.5W at 102 hours (tropical character supported by narrow swath of 26 deg C Gulf Stream water and fast northeast motion of surface low which reduces the effect of westerly shear induced by the upper trough)… becomes more elongated as a classical non-tropical frontal low near 40N-60W by 117 hours
1200Z NAVGEM Model Run...
**For Subtropical Storm Wanda…undergoes a cyclonic loop over the next 54 hours… afterwards accelerates northeast and reaches 50N-32W at 120 hours as a remnant non-tropical frontal cyclone.
**For area of interest #1…no development shown
**For area of interest #2… weakens to a surface trough near 17.5N-35W at 54 hours