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Tropical Storm Chris Forecast Discussion Number 8

2018-07-08 16:34:03| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Jul 08 2018 000 WTNT43 KNHC 081433 TCDAT3 Tropical Storm Chris Discussion Number 8 NWS National Hurricane Center Miami FL AL032018 1100 AM EDT Sun Jul 08 2018 A NOAA Hurricane Hunter plane has been traversing the circulation of Chris, and found that the wind field is gradually becoming better defined, while the central pressure has dropped to 1006 mb. Maximum winds so far from the SFMR are 40 kt, and this will be the intensity assigned to Chris in this advisory. Another reconnaissance aircraft will check the cyclone this afternoon. Recent high resolution satellite images indicate that the cloud pattern is becoming better organized with the low-level center now embedded within the convection. Chris is expected to be over a pool of warm water for the next 2 days and embedded within an environment of low shear. On this basis, the NHC forecast calls for Chris to become a hurricane in about 36 hours in agreement with the dynamical guidance and the HCCA model consensus. In about 4 days, Chris will be over 13 degree C water, and this should encourage extratropical transition. Since the steering currents surrounding Chris collapsed, the cyclone has barely moved since yesterday. These currents are foreast to remain light, so little motion is anticipated during the next 2 days. A mid-level trough forecast to swing eastward across the eastern United States will provide enough forcing to kick Chris northeastward with increasing forward speed over the Atlantic beyond 72 hours. The NHC forecast is in the middle of the track guidance envelope and follows closely the corrected consensus. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 32.9N 75.0W 40 KT 45 MPH 12H 09/0000Z 33.0N 74.8W 50 KT 60 MPH 24H 09/1200Z 32.5N 74.8W 55 KT 65 MPH 36H 10/0000Z 32.5N 75.0W 65 KT 75 MPH 48H 10/1200Z 32.5N 75.0W 75 KT 85 MPH 72H 11/1200Z 34.5N 72.5W 80 KT 90 MPH 96H 12/1200Z 41.0N 66.0W 60 KT 70 MPH 120H 13/1200Z 50.0N 52.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Avila

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Tropical Storm Chris Forecast Discussion Number 7

2018-07-08 10:58:30| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Jul 08 2018 000 WTNT43 KNHC 080858 TCDAT3 Tropical Storm Chris Discussion Number 7 NWS National Hurricane Center Miami FL AL032018 500 AM EDT Sun Jul 08 2018 An Air Force Reserve reconnaissance aircraft has been investigating the cyclone early this morning, and found flight-level winds of 45 kt at 925 mb and believable SFMR surface winds of around 34 kt in the southeast quadrant. On this basis, the system has been designated as Tropical Storm Chris, the 3rd named storm of the 2018 Atlantic season. Although the winds associated with the tropical storm have increased a little, the overall organization of Chris has not changed much over the past few hours. The low-level center is still exposed to the north of a broken band of deep convection and the cyclone lacks an inner-core. Chris is located over very warm SSTs and will remain so for the next several days. While the broad nature of the cyclone's circulation and some moderate shear will likely limit the intensification rate over the next day or so, all of the intensity guidance indicates that Chris will become a hurricane within about 72-h. By day 4, the intensity forecast is more uncertain, and depends strongly on the timing of Chris crossing the Gulf Stream, since the cyclone is expected to continue to intensify as long as it remains over warm waters. Once extratropical transition begins, weakening should occur as the wind field broadens. The new intensity forecast is close to HCCA and IVCN through day 3, and slightly lower beyond that, closer to the previous forecast. The track guidance has once again made a large shift with the latest forecast cycle. While Chris is generally expected to continue to meander off the coast of the Carolinas for the next couple of days before accelerating to the northeast ahead of a deep-layer trough approaching from the northwest, the timing of this acceleration is highly uncertain. Nearly all of the dynamical models have now shifted to the south and west of their previous forecasts throughout most of the forecast period. The NHC track forecast has been adjusted in that direction, but now lies on the eastern side of the guidance envelope, and shows a faster motion than most of the models. Given the large run-to-run inconsistency of the guidance over the past 24 hours, I would prefer to wait to make a more significant change to the forecast until a more clear pattern emerges. The Air Force reconnaissance plane also measured winds to gale-force about 20 miles off the coast of North Carolina. These winds are associated with the tight pressure gradient between Chris and high pressure over the northeastern U.S. See products issued by the National Weather Service forecast offices for more details. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 33.0N 75.5W 35 KT 40 MPH 12H 08/1800Z 33.0N 75.4W 40 KT 45 MPH 24H 09/0600Z 32.8N 75.3W 45 KT 50 MPH 36H 09/1800Z 32.6N 75.1W 55 KT 65 MPH 48H 10/0600Z 32.7N 74.7W 60 KT 70 MPH 72H 11/0600Z 35.2N 71.5W 70 KT 80 MPH 96H 12/0600Z 41.5N 64.0W 70 KT 80 MPH 120H 13/0600Z 49.0N 54.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Tropical Storm Beryl Forecast Discussion Number 12

2018-07-08 10:53:59| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Jul 08 2018 000 WTNT42 KNHC 080853 TCDAT2 Tropical Storm Beryl Discussion Number 12 NWS National Hurricane Center Miami FL AL022018 500 AM AST Sun Jul 08 2018 A burst of deep convection developed over the eastern portion of Beryl's circulation just after the release of the previous advisory. The convective burst has expanded overnight and the earlier exposed center of the cyclone is now located near the northwestern edge of the convective cluster. Subjective Dvorak intensity estimates from TAFB and SAB are unchanged, and the initial intensity remains 40 kt for this advisory. An Air Force Reserve reconnaissance aircraft is currently en route to Beryl and should provide a better assessment of the cyclone's intensity this morning. The intensity forecast reasoning is unchanged from the previous advisory. Westerly vertical wind shear is expected to increase over Beryl during the next 24 to 36 h, and the cyclone will be moving into a drier mid-level environment. As a result, Beryl is expected to weaken and degenerate into a trough of low pressure over the eastern Caribbean Sea. However, the system will likely produce strong gusty winds and locally heavy rainfall across the Leeward Islands, the Virgin Islands, and Puerto Rico during the next few days. The tropical storm is moving quickly west-northwestward or 290/17 kt. Beryl should continue on this general heading with some increase in forward speed as it is steered by a strong mid-level ridge to the north. The track guidance remains in fairly good agreement but there has been some increase in the cross track spread at 24 and 36 h with the GFS and HWRF along the southern edge of the guidance and the ECMWF bracketing the northern side of the envelope. The NHC track is in the middle of the envelope, close to the various consensus models, and in best agreement with the HFIP corrected consensus. Key Messages: 1. Tropical storm warnings and watches are in effect for portions of the Lesser Antilles where Beryl is forecast to bring impacts from wind and rainfall to some of the islands beginning late today or tonight. 2. Although Beryl is forecast to degenerate into a trough of low pressure over the eastern Caribbean, the system is likely to produce strong gusty winds and locally heavy rainfall across the remainder of the Leeward Islands, the Virgin Islands, Puerto Rico, and Hispaniola through Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 13.7N 56.0W 40 KT 45 MPH 12H 08/1800Z 14.7N 58.8W 40 KT 45 MPH 24H 09/0600Z 15.9N 62.7W 35 KT 40 MPH 36H 09/1800Z 17.4N 66.8W 30 KT 35 MPH 48H 10/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Three Forecast Discussion Number 6

2018-07-08 04:34:54| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Jul 07 2018 000 WTNT43 KNHC 080234 TCDAT3 Tropical Depression Three Discussion Number 6 NWS National Hurricane Center Miami FL AL032018 1100 PM EDT Sat Jul 07 2018 The depression is gradually becoming better organized. Geostationary satellite and microwave images indicate that the center is located on the northern side of a convective burst and to the east of a broken curved band. The initial intensity is held at 30 kt, in agreement with the Dvorak classification from SAB and ADT values from CIMSS at the University of Wisconsin. This estimate also uses data from NOAA buoy 41002 located about 60 n mi south-southeast of the center. An Air Force reconnaissance aircraft is scheduled to investigate the system overnight, and it should provide a better estimate of the cyclone's intensity. Satellite fixes suggest that the depression has now stalled, as forecast. The cyclone is caught in very weak steering currents between two mid-level ridges and a mid- to upper-level trough to its north. A very slow southeastward motion is expected during the next couple of days as ridging builds to the north of the system. Thereafter, a sharp northeastward turn with an abrupt increase in forward speed is predicted when a deep-layer trough approaches the cyclone. The NHC track forecast is adjusted a little to the south of the previous one in the short term based on the latest guidance. The depression is presently over the warm waters of the Gulf Stream Current and it will remain over these warm SSTs during the next few days. In addition, light to moderate wind shear and perhaps some baroclinic forcing from the approaching trough should allow the cyclone to steadily strengthen during the next few days. The NHC intensity forecast is slightly higher than the previous one, and near the middle of the guidance envelope. Extratropical transition is forecast to occur in a little more than 4 days when the system is expected to cross the north wall of the Gulf Stream current and move over very cold waters. Although the depression is expected to remain offshore of the North Carolina coastline, the tight pressure gradient between the depression and high pressure over the northeastern U.S. is expected to produce gale-force winds over Pamlico and Albemarle Sounds. See products issued by the National Weather Service forecast offices for more details. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 32.9N 75.1W 30 KT 35 MPH 12H 08/1200Z 32.8N 74.9W 40 KT 45 MPH 24H 09/0000Z 32.6N 74.6W 45 KT 50 MPH 36H 09/1200Z 32.4N 74.3W 50 KT 60 MPH 48H 10/0000Z 32.3N 73.9W 55 KT 65 MPH 72H 11/0000Z 34.5N 71.0W 70 KT 80 MPH 96H 12/0000Z 41.0N 63.0W 70 KT 80 MPH 120H 13/0000Z 49.0N 53.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Tropical Storm Beryl Forecast Discussion Number 11

2018-07-08 04:33:56| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Jul 07 2018 000 WTNT42 KNHC 080233 TCDAT2 Tropical Storm Beryl Discussion Number 11 NWS National Hurricane Center Miami FL AL022018 1100 PM AST Sat Jul 07 2018 Beryl is currently comprised of a small swirl of low- to mid-level clouds with isolated patches of deep convection near and east of the center. Satellite intensity estimates have decreased a little since the previous advisory, and based on them the initial intensity is set to a possibly generous 40 kt. The initial motion is 290/16. A strong low- to mid-level subtropical ridge north of Beryl should steer the system quickly west-northwestward during the next 36-48 h, and the track guidance is in excellent agreement on this. So, the new track forecast is an update of the previous forecast and lies near the center of the track guidance envelope. Westerly vertical wind shear is forecast to increase over Beryl during the next 48 h, and the cyclone will also be moving into a drier and more stable air mass. Based on this, the official intensity forecast calls for continued weakening, with Beryl forecast to weaken to a depression just after moving through the Lesser Antilles and then degenerate into a tropical wave just after 36 h. It should be noted that the official forecast is based on the premise that enough convection will return to the system to partly sustain it, and if this does not happen Beryl could weaken to a wave sooner than currently forecast. However, it should also be noted that even as an open wave the system will likely produce gusty winds and locally heavy rainfall across the Leeward Islands and portions of the Greater Antilles during the next several days. Key Messages: 1. Beryl continues to weaken, but there is still a chance of some islands in the Lesser Antilles receiving direct impacts from wind and rainfall, where tropical storm warnings and watches remain in effect. Gusty winds and locally heavy rainfall will also be possible across the remainder of the Leeward Islands, the Virgin Islands, Puerto Rico, and Hispaniola through early next week. 2. Due to its very small size, there is greater-than-usual uncertainty in the analysis of Beryl's current intensity, and confidence in the official intensity forecast is also lower than normal. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 13.1N 54.3W 40 KT 45 MPH 12H 08/1200Z 14.0N 56.8W 35 KT 40 MPH 24H 09/0000Z 15.3N 60.5W 35 KT 40 MPH 36H 09/1200Z 16.6N 64.5W 30 KT 35 MPH 48H 10/0000Z...DISSIPATED $$ Forecaster Beven

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