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Hurricane Chris Forecast Discussion Number 20

2018-07-11 16:59:19| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Jul 11 2018 576 WTNT43 KNHC 111459 TCDAT3 Hurricane Chris Discussion Number 20 NWS National Hurricane Center Miami FL AL032018 1100 AM AST Wed Jul 11 2018 The IR signature of Chris has fluctuated substantially this morning. The eye became obscured by clouds shortly after sunrise, and an SSMIS overpass at 1120 UTC indicated that the vortex had become tilted, with the mid-level eye displaced to the east of the low-level center of circulation. Since that time, however, the eye has once again become more distinct in visible and IR imagery. Dvorak estimates from all agencies had decreased markedly at 1200 UTC but given the improvement of the cloud pattern since then, the initial intensity has been lowered only slightly, to 85 kt. For the next 12 hours or so, the hurricane will be approaching and crossing the warm waters of the Gulf Stream, and no further weakening is expected. In fact it is possible that Chris could even briefly re-intensify, as shown by some of the intensity guidance, although this is not explicitly shown in the forecast. Once the hurricane crosses the northern wall of the Gulf Stream in about 24 hours, all of the dynamical models indicate that Chris will quickly acquire extratropical characteristics and rapidly weaken while its wind field becomes more spread out. Given the lower initial intensity, the new NHC intensity forecast is slightly lower than the previous one for the first 36 hours, but very similar thereafter, and is close to a consensus of the global and hurricane dynamical models. Almost no change has been made to the track forecast. Chris should continue accelerating toward the northeast ahead of an approaching mid-level trough over the next couple of days. By 96 hours, all of the global models forecast that Chris will begin to interact with another extratropical low, which should cause Chris to slow down, before the two lows eventually merge by day 5. The global models are still in very good agreement on the track of Chris, especially for the first 72 h of the forecast and confidence remains high in the track forecast. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 36.4N 67.8W 85 KT 100 MPH 12H 12/0000Z 38.7N 64.6W 85 KT 100 MPH 24H 12/1200Z 42.7N 59.6W 75 KT 85 MPH 36H 13/0000Z 46.9N 53.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 13/1200Z 50.3N 45.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 14/1200Z 56.8N 26.1W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 15/1200Z 62.0N 16.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 16/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Chris Forecast Discussion Number 19

2018-07-11 10:39:41| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Jul 11 2018 156 WTNT43 KNHC 110839 TCDAT3 Hurricane Chris Discussion Number 19 NWS National Hurricane Center Miami FL AL032018 500 AM AST Wed Jul 11 2018 Chris continues to have a very distinct eye, but the surrounding convection is not as strong as a few hours ago. Dvorak T-numbers are either steady or lower, so the initial intensity is kept at 90 kt in this advisory. Chris has the opportunity to strengthen a little during the next 12 to 18 hours while is moving over the Gulf Stream or warm waters. After that time, the hurricane will move over increasingly cold waters, and it should begin to acquire extratropical characteristics as it passes south of Newfoundland. Satellite fixes indicate that Chris has increased its forward speed, and is now moving toward the northeast or 050 degrees at 19 kt. The hurricane is already embedded withing the fast flow ahead of a large mid-level trough, and this pattern should continue to steer the hurricane northeastward over the open Atlantic with additional increase in forward speed. Models are in remarkably good agreement and consequently the guidance envelope is quite tight. This increases considerably the confidence in the track forecast. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 35.3N 69.9W 90 KT 105 MPH 12H 11/1800Z 37.2N 67.1W 95 KT 110 MPH 24H 12/0600Z 40.9N 62.1W 90 KT 105 MPH 36H 12/1800Z 45.0N 56.8W 75 KT 85 MPH 48H 13/0600Z 48.5N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 14/0600Z 55.5N 30.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 15/0600Z 63.0N 15.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 16/0600Z...DISSIPATED $$ Forecaster Avila

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Hurricane Chris Forecast Discussion Number 18

2018-07-11 04:44:09| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Tue Jul 10 2018 001 WTNT43 KNHC 110244 TCDAT3 Hurricane Chris Discussion Number 18 NWS National Hurricane Center Miami FL AL032018 1100 PM EDT Tue Jul 10 2018 Chris has been rapidly intensifying since the center moved out of the area of upwelled cold water about 18 h ago, likely due to an inner core convective ring seen earlier in microwave imagery becoming a fully-developed eyewall as the cyclone encountered warmer water. Satellite intensity estimates from SAB and TAFB at 00Z were 90 kt and 77 kt, and the CIMSS SATCON technique estimate was 90 kt. Based on this and a subsequent increase in organization, the initial intensity is increased to a possibly conservative 90 kt. The initial motion remains 050/9. Chris is becoming embedded in the mid-latitude westerlies between the subtropical ridge to the southeast and a large deep-layer trough over eastern Canada and the northeastern United states. The combination of these features should cause Chris to accelerate northeastward into the North Atlantic through 96 h, passing near southeastern Newfoundland in about 48 h. The new forecast track is a blend of the previous track and the HCCA and TVCN consensus models, and it is a little faster than the previous forecast. The eye of Chris is about to move over an area of slightly cooler water south of the core of the Gulf Stream, and this will likely slow the intensification rate. Otherwise, conditions appear favorable for intensification for the next 18-24 h, and the intensity forecast shows a little more strengthening before Chris moves north of the Gulf Stream. Extratropical transition should begin after Chris moves north of the Gulf Stream and be complete before the cyclone passes near southeastern Newfoundland. After that, the extratropical low should gradually decay as it crosses the North Atlantic. The new intensity forecast is increased from the previous forecast for the first 36 h based on current trends, and it has been lowered from the previous forecast between 72-120 h based on the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 34.2N 71.4W 90 KT 105 MPH 12H 11/1200Z 35.8N 69.1W 95 KT 110 MPH 24H 12/0000Z 38.8N 64.8W 95 KT 110 MPH 36H 12/1200Z 42.8N 59.4W 80 KT 90 MPH 48H 13/0000Z 46.6N 53.1W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 14/0000Z 53.0N 36.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 15/0000Z 57.0N 19.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 16/0000Z 61.5N 10.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane Chris Forecast Discussion Number 17

2018-07-10 22:54:06| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Tue Jul 10 2018 951 WTNT43 KNHC 102054 TCDAT3 Hurricane Chris Discussion Number 17 NWS National Hurricane Center Miami FL AL032018 500 PM EDT Tue Jul 10 2018 Reports from an Air Force Reserve hurricane hunter aircraft indicate that Chris has finally attained hurricane status, making it the second hurricane thus far this season, which is ahead of climatology by more than six weeks. The aircraft found 850-mb flight-level winds of 88 kt in the southeastern quadrant, along with SFMR winds of 73-77 kt. Dropsondes in the the same area found equivalent surface winds of 73-74 kt, and the most recent central pressure observed was 980 mb. Furthermore, satellite intensity estimates are a consensus T4.5/77 kt from TAFB, SAB, and UW-CIMSS ADT, based on a well-defined 20-nmi-diameter clear eye. These data support a solid 75-kt advisory intensity. The initial motion is a slightly faster 050/09 kt. Chris is north of a narrow subtropical ridge, and water vapor imagery also indicates that Chris is beginning to feel the influence of a digging trough over the northeastern U.S. and Mid-Atlantic states. The combination of these two features should gradually accelerate the hurricane northeastward at a faster forward speed through 96 hours. By the time Chris passes well southeast of Nova Scotia in 36 hours or so, the hurricane will be moving at a forward speed of more than 25 kt. On the new forecast track, Chris is still expected to move near or over southeastern Newfoundland in about 48-60 hours. The latest model guidance has a much larger spread in both cross-track and along-track motions. To smooth out these differences, the new forecast track is down the middle of the tighter HCCA, FSSE, and TVCN consensus model suite. Now that Chris has moved away from the cold upwelling region, some additional intensification is forecast for the next 12 hours or so due to 27-28 deg C SSTs beneath the cyclone and the well-established current outflow pattern that is expected to persist during that time. Slow weakening should begin shortly after Chris peaks in intensity due to the cyclone moving over cooler waters, creating some modest upwelling as a result. By 36 hours, Chris will have moved well north of the Gulfstream and be moving over SSTs colder than 15 deg C. The combination of the much colder water and southwesterly vertical wind shear in excess of 30 kt should induce a rapid transition to an extratropical cyclone. The official intensity forecast is above the intensity guidance through 12 hours, and then shows weakening after that similar to the LGEM and IVCN models. Now that Chris is moving away from the United States, the previously scheduled aircraft mission for 11/0600 UTC has been canceled. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 33.7N 72.4W 75 KT 85 MPH 12H 11/0600Z 34.9N 70.7W 85 KT 100 MPH 24H 11/1800Z 37.1N 67.4W 80 KT 90 MPH 36H 12/0600Z 40.5N 62.6W 75 KT 85 MPH 48H 12/1800Z 44.7N 57.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 13/1800Z 51.0N 41.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/1800Z 55.2N 22.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 15/1800Z 59.0N 12.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Chris Forecast Discussion Number 16

2018-07-10 16:53:03| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Jul 10 2018 034 WTNT43 KNHC 101452 TCDAT3 Tropical Storm Chris Discussion Number 16 NWS National Hurricane Center Miami FL AL032018 1100 AM EDT Tue Jul 10 2018 During the past 6 hours, Chris has developed a well-defined eye in both satellite and radar imagery at times, with a diameter that has varied in size from 30 nmi to the present 20 nmi. The overall convective pattern has also become more symmetrical with well-established outflow present in all quadrants. Satellite intensity estimates are T3.5/55 kt from TAFB, and T4.0/65 kt from SAB and UW-CIMSS ADT, and Chris certainly has the satellite appearance of being a hurricane. However, the intensity is being maintained at 60 kt for this advisory due to significant cold upwelling that has occurred beneath the cyclone when Chris was moving slowly during the previous 48 hours. The colder waters have likely stabilized the boundary layer, which has inhibited stronger winds aloft from mixing down to the surface. The cold upwelling is supported by sea-surface temperature (SST) data from nearby NOAA Buoy 41002, which has shown 6 deg F of cooling during the past 48 hours, and is currently sitting at 76F. An Air Force Reserve reconnaissance aircraft is scheduled to investigate Chris this afternoon to provide a better intensity estimate. Recent satellite and radar fixes indicate that Chris is finally moving northeastward at a faster forward speed, and the initial motion estimate is now 050/08 kt. The narrow subtropical ridge to the southeast of the cyclone is getting pushed northward by the remnants of Beryl, which has helped to finally nudge Chris toward the northeast. A further increase in forward speed is expected as a strong deep-layer trough digs southeastward along the U.S. east coast, accelerating the cyclone at forward speeds of 25-30 kt by 48 hours and beyond. Chris is forecast to pass well southeast of Nova Scotia in a couple of days, and move near or over southeastern Newfoundland in about 60 hours. The NHC track guidance remains in good agreement on the evolving steering flow regime, but there continues to be some pronounced speed differences. The new NHC track forecast is similar to the previous advisory, and lies close to the consensus models HCCA, FSSE, and TVCN. My best estimate, based on the data from Buoy 41002, is that significant upwelling likely occurred within the 30-kt wind radii while Chris was nearly stationary. Assuming that that is the case, then Chris will be moving over warmer waters shortly, which should allow for an increase in convection to occur and also for winds aloft to better mix downward to the surface. The vertical wind shear is forecast to remain modest at 10-15 kt for the next 24 hours, so gradual intensification is expected during that time. By 48 hours, Chris will have crossed over the north wall of the Gulfstream and be moving over SSTs colder than 20 deg C, which will combine with strong southwesterly wind shear, and cause Chris to rapidly transition to an extratropical cyclone. The official intensity forecast follows the FSSE intensity model through 36 hours, and then shows more significant weakening after that, similar to the SHIPS, LGEM, and HCCA models. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 33.1N 73.1W 60 KT 70 MPH 12H 11/0000Z 33.9N 71.9W 70 KT 80 MPH 24H 11/1200Z 35.6N 69.4W 75 KT 85 MPH 36H 12/0000Z 38.4N 65.5W 75 KT 85 MPH 48H 12/1200Z 42.0N 60.6W 65 KT 75 MPH 72H 13/1200Z 48.1N 49.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/1200Z 52.0N 31.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 15/1200Z 54.0N 18.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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