MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #24
Updated: Jun 7
*******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.**********
...SATURDAY JUNE 6 2020 6:09 PM EDT...
Tropical Storm Cristobal accelerates northward across the Gulf of Mexico from the Yucatan peninsula...poised to approach the United States Gulf coast this weekend...see Cristobal section below for details. See area of interest section below for potential subtropical cyclone development east of Bermuda in 3 to 5 days.
TROPICAL STORM CRISTOBAL...Southerly surface flow out ahead of the broad frontal low pressure area over the western United States...supported by the upper divergence zones of the pieces of energy south of Alaska and offshore of California that have recently merged into an impressive upper trough...continues to channel Tropical Storm Cristobal northward across the Gulf of Mexico and toward the United States Gulf coast. Cristobal has been in a battle with upper vorticity in the western Gulf of Mexico...which has blocked the western outflow of the storm and with its western convergence zone has produced dry sinking air that has been ingested into the core of Cristobal's circulation. Despite this...Cristobal has strengthened slightly to 50 mph max sustained winds over the last 24 hours almost as if its a hybrid...or a subtropical...storm...with non-tropical support coming from the eastern divergence zone of the upper vorticity...and the latent heat release of the thunderstorm bands well north and east of Cristobal's core producing enough latent heat and upper ridging off to the east to provide simultaneous tropical support with upper outflow.
The 1200Z GFS model run upper wind field suggested that the warm southerly surface flow steering Cristobal will cause the unfavorable cool core western Gulf upper vorticity to dissipate at least in the northwestern Gulf in the next 24 hours...becoming replaced with warm anticyclonic outflow directly over Cristobal's center as the longwave upper ridge approaching from western North America attempts to bridge with the upper ridging currently covering the east half of Cristobal. This could result in a more favorable upper wind pattern for thunderstorms to develop over Cristobal's core for additional strengthening just before landfall...and the early signs of this maybe starting to show on colorized infrared satellite with pockets of showers and thunderstorms developing at the core for the first time since Cristobal entered the Gulf of Mexico yesterday. So although I believe the window for Cristobal to become a category 1 hurricane has closed...I still forecast some additional strengthening while reverting back to my intensity forecast from posts #21 and #22 which peaked Cristobal at 60 mph max winds...which is also where the National Hurricane Center has been keeping the intensity forecast over the last few days.
After the center makes landfall over southeastern Louisiana around 24 hours from now...I support the idea of a northwestward lean in track as the current upper trough energy over eastern Canada will dive south and amplify over the northeastern United States due to the highly amplified nature of the western North America longwave upper ridge. This will position the western convergence zone of the upper trough and resulting surface ridge to the northeast of Cristobal...close enough for the ridge to add a west component to the storm track. Also in the upper layers the steering supports a west component as the western North America longwave upper ridge will be shifting eastward to a position directly north of Cristobal. The eastward shift of the longwave ridge will be from the kick supplied by the vigorous upper trough and large-scale surface frontal system currently developing over the western United States. Just after 72 hours...computer models increasingly suggest that the remants of Cristobal will align with the eastern upper divergence maximum of the western United States upper trough...resulting in the remnant circulation intensifying into a vigorous and possibly intense frontal cyclone that moves through the Great Lakes and into eastern Canada. Therefore wind impact to the Great Lakes region and Ontario looks increasingly likely in about 4 days.
Interests on the United States Gulf coast from Louisiana to the Florida panhandle should be rushing preparations to completion for coastal storm surge and wind impact as weather conditions will detereorate tonight in advance of Cristobal's approaching center...see bulletins on home page of this site for details on this and other post-landfall impacts that are expected.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Jun 6)...50 mph maximum sustained wind tropical storm centered in the Gulf of Mexico at 24.7N-90.2W
IOH 24 Hr Forecast (1800Z Jun 7)...60 mph maximum sustained wind tropical storm making landfall on the southeast Louisiana coast at 29N-90W
IOH 48 Hr Forecast (1800Z Jun 8)...35 mph maximum sustained wind tropical depression centered over northeastern Louisiana at 32N-92W
IOH 72 Hr Forecast (1800Z Jun 9)...Remnant frontal low pressure centered over northeastern Missouri at 38N-91W
AREA OF INTEREST #1...The National Hurricane Center in their 5-day tropical weather outlook has highlighted the central tropical Atlantic to the east of Bermuda as an area of interest for subtropical development. This is response to continued computer model solutions that show a surface low pressure area will develop in this area in about 3 days in response to current upper trough over eastern Canada diving southward and amplifying into a cut-off upper vortex in the Atlantic along the east side of the upper ridge emerging from western North America...as the upper ridge later amplifies in the eastern warm air advection zone of what is expected to be the remnant frontal cyclone of Cristobal moving into the Great Lakes region and Ontario Canada. The cold temperatures of the forecast cut-off upper vortex may allow for subtropical development despite central Atlantic water temperatures of 22 deg C in the central Atlantic region. However at this time I am only forecasting low 10% odds of subtropical cyclone formation as the forecast upper vortex is shown in the 1200Z GFS to become elongated and streteched southwest-to-northeast in the 72 to 96 hour timeframe by the ridge approaching from western North America moves into the northwest Atlantic. This could result in an elongated instead of consolidated surface ciruclation needed for subtropical development. Even though the upper vortex is shown to be circular again by 120 hours...its 200 mb height is forecast to be in the mid-1210s of dekameters. As the recent subtropical disturbance southeast of Bermuda showed on May 30...a mid-1210s dekameter upper vortex is cold enough to produce thunderstorms if water temps are in the mid-20s of deg C...not as certain about thunderstorm development with this disturbance with water temps slightly cooler at 22 deg C. Because the ridge as it enters the Atlantic will have a southwest lobe directly west of this system...the forward progress of this system toward Bermuda will be slow as the rest of the ridge tries to steer the system west. Not mentioning any impacts to Bermuda on the home page bulletins of this site till model solutions remain consistent...and it is possible that after 72 hours this system will be weakening directly below the center of the upper vortex where there is a lack of supportive divergence such that impacts to Bermuda would be minimal.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 7)...0% chance of subtropical cyclone formation (western Atlantic near 35N-70W)
IOH 48 Hr Outlook (1800Z Jun 8)...0% chance of subtropical cyclone formation (east of Bermuda near 32.5N-61W)
IOH 72 Hr Outlook (1800Z Jun 9)...10% chance of subtropical cyclone formation (east of Bermuda near 32.5N-55W)
IOH 96 Hr Outlook (1800Z Jun 10)...10% chance of subtropical cyclone formation (east of Bermuda near 32.5N-58W)
IOH 120 Hr Outlook (1800Z Jun 11)...10% chance of subtropical cyclone formation (Bermuda near 32.5N-65W)
...COMPUTER MODEL SUMMARY...
Source...National Weather Service Model Analyses and Guidance (https://mag.ncep.noaa.gov/)
1200Z GFS Model Run...For Tropical Storm Cristobal...in 24 hours has center of circulation just offshore of southeastern Louisiana...forecasts landfall over southeastern Louisiana at 37 hours...has remnant circulation of Cristobal crossing western Great Lakes region and entering eastern Canada as a large intensifying frontal cyclone at 96 hours. For area of interest #1...develops central Atlantic broad surface low at 32.5N-56W at 72 hours in response to current eastern Canada upper trough diving south and amplifying into the Atlantic...has surface low drift slowly northwest and weakened into a surface trough northeast of Bermuda in the vicinity of 35N-62.5W