Atlantic/2018/03L/Archive/8

Tropical Storm Chris Discussion Number 8

Wiki-Hurricanes Forecast Center

11:00 PM EDT Mon Jul 9 2018

Data from an NOAA reconnaissance aircraft currently sampling Chris this evening indicate that Chris has not moved much and still remains quasi-stationary, though the latest trend has been towards the southeast. After a morning of subsidence driven by dry continental maritime air and upwelled water, Chris has done well to build convection during the late-afternoon and into the nighttime hours. Infrared imagery shows an active core around a banding eye with a decently organized central cloud cover mostly displaced towards the southeast with some banding features to the southwest. Microwave data from a 2307Z SSMIS pass showed a nearly complete eyewall open to the north with central banding to the southwest. Reconnaissance data is confirming the elliptical eye spanning about 30 miles across.

Although the system appears to have organized, the NOAA aircraft wind data have not offered enough convincing evidence to change the intensity of Chris at this time. A southeast-northwest pass of the NOAA aircraft in an intensifying band of convection near the center sampled flight level winds of peaking at 57kt. Despite a tendency for lower values from NOAA 650mb flights compared to USAF 850mb flights, dropsonde data from the flight has largely verified the remote aircraft senors. Thus, the intensity for this advisory has been kept at a somewhat uncertain 60 kt wit no clear blended in-situ and satellite justification for a change, though objectively the recon data alone at this time would support 50-55 kt at face value.

No changes to the forecast philosophy for this advisory with the same steering factors still in play. Water vapor imagery shows a shortwave trough with a leading frontal edge now entering New England and the Mid-Atlantic United States. Models are in general agreement that this approaching trough will begin to steer Chris towards the northeast sometime tonight or late-morning Tuesday. Steering is fairly straightforward after that point as the system is carted poleward. Westerly polar flow enhanced by an extratropical cyclone associated with the same pivotal shortwave trough should curve Chris eastward before the tropical system is absorbed.

Chris is expected to become a hurricane sometime tonight as it continues to organize. Despite upwelled waters which have fallen even further to at least 25C as observed by a buoy in the southwestern quadrant of the tropical storm, convection continues to develop, perhaps aided by decent divergent flow along the frontal boundary. Tropically-supportive conditions improve within a 24-hour window should Chris take advantage of the anomolously warm Gulf Stream/US East Coast waters before extratropical processes begin to take over in cooler waters. Some strengthening is depicted during this time before steady weakening occurs out to 96 hours. Have lowered peak intensity somewhat in alignment with current statistical model guidance.

Interests in the Canadian Maritimes are strongly advised to monitor this system closely and follow guidance from local authorities as Chris is expected to bring strong winds to Nova Scotia and Newfoundland beginning Thursday and continuing through Friday. Newfoundland is likely to see hurricane-force wind gusts Friday with a projected landfall from an extratropically transitioning Chris.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 60KT 70MPH

12H 10/1200Z 70KT 80MPH

24H 11/0000Z 80KT 90MPH

36H 11/1200Z 80KT 90MPH

48H 12/0000Z 70KT 80MPH

72H 13/0000Z 65KT 70MPH...EXTRATROPICAL/NEAR NEWFOUNDLAND

96H 14/0000Z 45KT 50MPH...EXTRATROPICAL

120H 15/0000Z ... DISSIPATED