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Tropical Storm Chris Forecast Discussion Number 15

2018-07-10 10:47:59| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Jul 10 2018 000 WTNT43 KNHC 100847 TCDAT3 Tropical Storm Chris Discussion Number 15 NWS National Hurricane Center Miami FL AL032018 500 AM EDT Tue Jul 10 2018 The satellite presentation of Chris has improved overnight with an increase in convective banding and the recent development of a banding eye. An earlier NOAA and an overnight Air Force Reserve aircraft have noted the presence of a ragged 25 n mi wide eye, which can also be seen in NWS WSR-88D radar imagery from Morehead City, North Carolina. Despite the increase in organization the Air Force aircraft did not find winds to support hurricane strength. In fact, the plane only measured peak 850 mb flight level winds of 66 kt and SFMR winds of around 50 kt. However, there is likely some undersampling as the plane only made one pass through each quadrant. Therefore the initial remains 60 kt, which is compromise between the most recent satellite estimates and the lower reconnaissance data. The aircraft did report that the pressure has fallen to 993 mb. Recent satellite and aircraft fixes suggest that Chris may be beginning its much anticipated northeastward motion, albeit very slow at the moment. A large mid-latitude trough is forecast to drop southeastward over eastern Canada and the northeastern United States which should begin to steer Chris on a faster northeastward heading over the next day or so. As the trough deepens, Chris should accelerate further as it becomes embedded within deep-layer southwesterly flow ahead of the trough. Chris is forecast to pass well southeast of Nova Scotia in a couple of days, then move near or over southeastern Newfoundland in about 72 hours. The track guidance remains in good agreement on this scenario, but some speed differences remain. The updated NHC track forecast is similar to the previous advisory and lies between the slower ECMWF and the various consensus aids. As Chris begins to move northeastward, it will be leaving the area of upwelled cooler waters and traversing warm SSTs during the next 24 to 36 h. This should result in strengthening and Chris is expected to become a hurricane later today. By 48 h, Chris will be moving over colder waters north of the Gulf Stream and begin interacting with a frontal system. Extratropical transition is expected to be complete in about 60-72 h, and the extratropical low is forecast to gradually weaken after passing Newfoundland. The new NHC intensity forecast is closest to the Florida State Superensemble, which is a little higher than the statistical guidance. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 32.6N 73.9W 60 KT 70 MPH 12H 10/1800Z 33.1N 73.2W 70 KT 80 MPH 24H 11/0600Z 34.4N 71.4W 75 KT 85 MPH 36H 11/1800Z 36.5N 68.2W 80 KT 90 MPH 48H 12/0600Z 39.7N 64.0W 75 KT 85 MPH 72H 13/0600Z 46.5N 53.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 14/0600Z 50.7N 38.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 15/0600Z 53.0N 23.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Chris Forecast Discussion Number 14

2018-07-10 04:58:58| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Jul 09 2018 000 WTNT43 KNHC 100258 TCDAT3 Tropical Storm Chris Discussion Number 14 NWS National Hurricane Center Miami FL AL032018 1100 PM EDT Mon Jul 09 2018 Reports from a NOAA Hurricane Hunter aircraft indicate that Chris has changed little in strength during the past several hours. The aircraft has reported maximum flight-level of 63 kt at 700 mb to the southwest of the center, along with a somewhat-uncertain maximum SFMR surface wind estimate of 61 kt. The latest reported central pressure is 995 mb. Based on these, the initial intensity will be held at a possibly generous 60 kt. The aircraft also reported that a partial eyewall of 20-30 n mi diameter has formed, but has not yet been able to close off. Chris has moved little since the last advisory, as it remains trapped in a break in the subtropical ridge. A large mid-latitude trough is forming over eastern Canada and the northeastern United States, and as this system develops southward it should break down the ridge and steer Chris to the northeast after about 12 h, with an increasing forward speed expected thereafter as the tropical cyclone enters the mid-latitude westerlies. Chris should pass east of the Canadian Maritimes in about 72 h, then pass near or over southeastern Newfoundland between 72-96 h. The track guidance generally agrees with this scenario, although some spread remains in the forecast forward speed. The new forecast track is an update of the previous forecast and lies near the various consensus models. The sea surface temperature at NOAA buoy 41002, located 45 n mi southwest of the center of Chris, has dropped to near 25C, and it is possible that the temperatures are colder under the center. This ocean cooling, due to upwelling caused by the slow motion of the storm, has likely slowed the intensification of Chris despite an otherwise favorable environment and storm structure. Significant intensification now appears unlikely until the cyclone actually starts moving. Based on this and the forecast track, the new intensity forecast will delay Chris' intensification into a hurricane until the 18-24 h point. After that, Chris should strengthen until it moves north of the Gulf Stream and starts to merge with a frontal system. Extratropical transition is expected to be complete by 72 h, with the extratropical low gradually decaying as it moves across the north Atlantic. The new intensity forecast follows the overall trend of the intensity guidance except during the first 12 h. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 32.3N 74.3W 60 KT 70 MPH 12H 10/1200Z 32.6N 73.9W 60 KT 70 MPH 24H 11/0000Z 33.5N 72.7W 70 KT 80 MPH 36H 11/1200Z 35.1N 70.4W 80 KT 90 MPH 48H 12/0000Z 37.7N 66.6W 80 KT 90 MPH 72H 13/0000Z 44.0N 59.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 14/0000Z 49.0N 47.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/0000Z 52.0N 31.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Tropical Storm Chris Forecast Discussion Number 13

2018-07-09 22:52:51| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Mon Jul 09 2018 000 WTNT43 KNHC 092052 TCDAT3 Tropical Storm Chris Discussion Number 13 NWS National Hurricane Center Miami FL AL032018 500 PM EDT Mon Jul 09 2018 Satellite, Doppler radar, and Air Force reconnaissance aircraft data this afternoon indicate that inner-core region of Chris has improved in organization, and that the cyclone has strengthened some. A peak 850-mb flight-level of 73 kt was measured in the southwestern quadrant along with slightly rain-contaminated SFMR surface winds of 53-59 kt. The central pressure has also decreased to 997-996 mb. Based on these data, the intensity has been increased to 60 kt for this advisory. NOAA and Air Force Reserve reconnaissance fixes thus far today indicate that Chris has essentially remained nearly stationary for the past 9 hours. Steering should remain weak for the next 24 hours or so due to the cyclone being trapped in a large break in the subtropical ridge, thus little motion is expected. However, by 36 hours and beyond, a deepening mid-latitude trough along the U.S. Northeast and mid-Atlantic coasts is forecast to gradually lift out Chris to the northeast, with more significant northeastward acceleration occurring by 72 hours and beyond. Chris is expected to move across the offshore waters of Atlantic Canada on days 4 and 5 as a powerful extratropical low, possibly passing over southeastern Newfoundland around the 96-hour time period. The NHC model guidance continues to show fairly significant along-track or speed differences. As a result, the official forecast track remains close to the consensus track models TVCN, HCCA, and FSSE. A band of very dry mid-level air with humidity values less than 45 percent has completely encircled Chris, and the cyclone is beginning to take on the appearance of an annular formed hurricane with a new 15-nmi-diameter, cloud-filled eye having within the central convective cloud mass during the past couple of hours. The well-defined inner-core wind field, in conjunction with the with SSTs near 28 deg C and a low vertical wind shear regime, should act to maintain inner-core convective development. The result should be gradual strengthening over the next day or, with Chris becoming a hurricane later tonight or Tuesday morning and reaching a peak intensity of 80 kt by 36 hours. Gradual weakening should commence by 48 hours when the cyclone will be moving over cooler water and southwesterly wind shear begins to increase to near 20 kt. By 72 hours and beyond, Chris will be over SSTs less than 20 deg C and within stronger shear environment ahead of an approaching deep-layer trough, which will induce a rapid transition to a powerful extratropical cyclone before the system approaches Newfoundland in about 96 hours. The extratropical low is forecast to merge with a cold front in 96-120 hours, which should enhance the extratropical transition process. The new NHC intensity forecast is just an update of previous two advisories, and similar to the intensity model FSSE, which is sightly higher than the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 32.2N 74.4W 60 KT 70 MPH 12H 10/0600Z 32.3N 74.3W 65 KT 75 MPH 24H 10/1800Z 32.8N 73.6W 75 KT 85 MPH 36H 11/0600Z 34.0N 71.9W 80 KT 90 MPH 48H 11/1800Z 36.1N 69.0W 75 KT 85 MPH 72H 12/1800Z 42.2N 61.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 13/1800Z 48.3N 50.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 14/1800Z 52.0N 35.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Chris Forecast Discussion Number 12

2018-07-09 16:55:49| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Mon Jul 09 2018 000 WTNT43 KNHC 091455 TCDAT3 Tropical Storm Chris Discussion Number 12 NWS National Hurricane Center Miami FL AL032018 1100 AM EDT Mon Jul 09 2018 A NOAA reconnaissance aircraft investigating Chris this morning has found little change in the overall structure of the cyclone. The peak 8000-ft wind measured was 60 kt to the south of the center along with a 51-kt SFMR surface wind. The minimum pressure has also remained steady at 999 mb during the entire mission which is still ongoing. Although an eye-like feature has briefly appeared in WSR-88D Doppler radar data from Morehead City and in satellite imagery as well, the convection surrounding that feature has been mostly shallow and ragged. Based on these data, the intensity remains at 50 kt for this advisory. Air Force and NOAA reconnaissance fixes the past several hours and satellite fixes indicate that Chris has moved little. Steering currents are forecast to remain weak for the next 24 hours or so, resulting in continued slow movement. By 36 hours, however, a shortwave trough is forecast to dig southeastward out of Canada and into the northeastern U.S. and mid-Atlantic states, which should help to eject the cyclone northeastward. By 48 hours and beyond, the shortwave trough will help to amplify a deep-layer trough near the U.S. east coast, causing Chris to accelerate northeastward toward the Atlantic Canada region. The NHC model guidance continues to show little cross-track differences, but fairly significant along-track or speed differences. As a result, the official forecast track remains close to the consensus track models. A narrow band of dry mid-level air has wrapped all the way around and into the inner-core region, which has caused some erosion of the associated convection, along with some upwelling. However, the reconnaissance wind data indicated that Chris has a relatively small radius of maximum winds (RMW) of 15 nmi to the south and about 25 nmi to the north. This well-defined inner-core wind field, coupled with warm water and low vertical shear conditions, should enable the cyclone to mix out the dry air later today and tonight, which will allow for strengthening to begin. The intensification process should be steady at a near-normal rate for the next 36 hours or so, followed by gradual weakening in a few days as the waters beneath Chris begin to cool and the wind shear increases from the southwest. By 72 hours and beyond, Chris will be over much colder water (SSTs less than 20 deg C) and within a high shear environment of 30 kt or more, which will induce a rapid transition to a powerful extratropical cyclone as the system approaches Newfoundland. The extratropical low is forecast to interact or merge with a strong cold front by 96 hours when the cyclone is near Newfoundland, which will enhance the extratropical transition process. The new intensity forecast is similar to the previous advisory and shows Chris reaching hurricane strength by Tuesday. Chris could reach a peak intensity of 80 kt between the 36 and 48 hour time periods before weakening begins shortly thereafter. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 32.2N 74.5W 50 KT 60 MPH 12H 10/0000Z 32.3N 74.4W 55 KT 65 MPH 24H 10/1200Z 32.4N 74.3W 65 KT 75 MPH 36H 11/0000Z 33.3N 73.0W 75 KT 85 MPH 48H 11/1200Z 34.8N 70.9W 75 KT 85 MPH 72H 12/1200Z 40.5N 64.0W 70 KT 80 MPH 96H 13/1200Z 47.0N 55.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 14/1200Z 51.1N 41.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Chris Forecast Discussion Number 11

2018-07-09 10:43:15| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Jul 09 2018 000 WTNT43 KNHC 090843 TCDAT3 Tropical Storm Chris Discussion Number 11 NWS National Hurricane Center Miami FL AL032018 500 AM EDT Mon Jul 09 2018 After the expansion of deep convection during the evening it appears that some drier air has been entrained into the circulation which has caused a general warming of the cloud tops and some erosion of the deep convection overnight. However, the banding remains well organized and the overall structure of the cyclone has not changed appreciably. An Air Force Reserve reconnaissance aircraft investigating the system has found that the minimum pressure has dropped to 999 mb, but the flight-level and SFMR winds still support an initial intensity of 50 kt. Recent aircraft and satellite fixes indicate that Chris is drifting southward. Steering currents are expected to remain quite weak during the next 36 hours as Chris is situated between a couple of mid-level highs and a mid- to upper-level trough to its northeast. By late Tuesday, a deep-layer trough moving across the Great Lakes region should begin to lift Chris out toward the northeast. The cyclone is predicted to accelerate northeastward during the remainder of the forecast period as it gets caught in strong southwesterly flow ahead of the aforementioned trough. The track models are in good agreement on this general scenario but there are some differences in how fast Chris accelerates over the western Atlantic. The new NHC track forecast has been shifted slightly northwestward to be in better agreement with the latest guidance, and it remains near the model consensus to account for the forward speed differences among the various track models. The cyclone should be able to mix out the dry air that it entrained while it is located over warm water and in light to moderate vertical wind shear conditions. This should allow strengthening during the next couple of days, but there could be some upwelling beneath the slow moving cyclone which could temper the rate of intensification. The new NHC track forecast shows a slightly slower rate of deepening during the next 24 to 36 h, but still forecasts Chris to become a hurricane later today or tonight, and reach about the same peak intensity as shown in the previous advisory. The hurricane should become extratropical by 96 h, and the global models indicate that steady weakening will occur after that time. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 32.4N 74.6W 50 KT 60 MPH 12H 09/1800Z 32.4N 74.6W 55 KT 65 MPH 24H 10/0600Z 32.5N 74.7W 65 KT 75 MPH 36H 10/1800Z 33.0N 73.9W 70 KT 80 MPH 48H 11/0600Z 34.2N 72.2W 80 KT 90 MPH 72H 12/0600Z 39.0N 66.4W 80 KT 90 MPH 96H 13/0600Z 45.5N 59.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0600Z 49.5N 49.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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