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Tropical Storm GRACE Forecast Discussion Number 12

2015-09-08 10:39:51| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE SEP 08 2015 000 WTNT42 KNHC 080839 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 500 AM AST TUE SEP 08 2015 The deep convection that developed during the evening hours has expanded in coverage overnight, but very little banding or overall organization of the thunderstorm activity exists. The initial wind speed remains 35 kt, which is supported by a TAFB subjective Dvorak intensity estimate and a UW/CIMSS ADT current intensity number. The intensity forecast reasoning remains unchanged from the previous advisory. Increasing southwesterly to westerly vertical wind shear and dry mid-level air along the forecast track should cause Grace to weaken during the next few days. Grace is forecast to weaken to a tropical depression later today, and become a remnant low within the next couple of days. The system is expected to degenerate to a trough by the time it reaches the eastern Caribbean. Given the fast motion of the system and the expected hostile conditions, this could occur much sooner than shown in the official forecast. The initial motion estimate remains 275/17 kt. Grace or its remnant is forecast to continue moving quickly westward to the south of a low- to mid-level ridge that is over the central Atlantic. The model guidance is again tightly clustered and the NHC forecast is essentially an update of the previous track. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 14.1N 41.0W 35 KT 40 MPH 12H 08/1800Z 14.2N 43.7W 30 KT 35 MPH 24H 09/0600Z 14.5N 47.2W 30 KT 35 MPH 36H 09/1800Z 14.9N 50.6W 30 KT 35 MPH 48H 10/0600Z 15.3N 54.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 11/0600Z 16.3N 60.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/0600Z...DISSIPATED $$ Forecaster Brown

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Hurricane LINDA Forecast Discussion Number 9

2015-09-08 04:57:05| National Hurricane Center (East Pacific)

Issued at 900 PM MDT MON SEP 07 2015 000 WTPZ45 KNHC 080256 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152015 900 PM MDT MON SEP 07 2015 Linda's cloud pattern has become less organized since earlier today. A 0116 UTC SSMIS pass showed the low-level center on the northeastern tip of the deepest convection, to the northeast of previous estimates. The distribution of convection in the cyclone's central dense overcast has also become somewhat asymmetric. The current structural organization of the cyclone suggests that moderate northeasterly shear over the cyclone has been a factor in the system's evolution today. The initial intensity estimate is lowered to 80 kt, on the lower end of a blend of Dvorak Final T- and CI-numbers from TAFB and SAB. Although most large-scale factors could favor some additional intensification, the current arrested development is likely to continue as Linda continues to feel the effect of northeasterly shear associated with an upper-level anticyclone to its northeast. Within 24 to 36 hours, Linda will be traversing marginally cool waters and ingesting drier and more stable air, which should result in slow but steady weakening. The rate of weakening should become rapid in 2 to 3 days once Linda reaches even colder waters and thermodynamic factors become increasingly more hostile. Remnant low status is now predicted in 3 days. The new NHC forecast is lowered relative to the previous one and generally lies near the multi-model consensus. Linda has been moving northwestward or 325/09 throughout the day. The cyclone is moving in a deep-layer southeasterly flow on the southwestern periphery of a subtropical ridge located over northern Mexico. The ridge is forecast to weaken during the next couple of days, which should result in a decrease in Linda's forward speed while it maintains about the same heading. The low-level trades should begin to steer the cyclone west-northwestward in 2 to 3 days, and then westward after that time as Linda weakens and becomes an increasingly shallower cyclone. The NHC track forecast has been adjusted to the right of the previous one, based on a re-positioning of the center based on recent microwave fixes. Although Linda is forecast to remain well offshore of the Baja California peninsula, large swells are expected to affect portions of the west coast of that peninsula during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 18.8N 112.8W 80 KT 90 MPH 12H 08/1200Z 20.4N 113.9W 75 KT 85 MPH 24H 09/0000Z 21.8N 115.0W 70 KT 80 MPH 36H 09/1200Z 23.1N 116.0W 60 KT 70 MPH 48H 10/0000Z 24.4N 117.2W 50 KT 60 MPH 72H 11/0000Z 25.9N 119.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 12/0000Z 26.3N 121.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 13/0000Z 26.3N 124.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Tropical Storm GRACE Forecast Discussion Number 11

2015-09-08 04:52:53| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON SEP 07 2015 000 WTNT42 KNHC 080252 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 1100 PM AST MON SEP 07 2015 After being devoid of any significant convection near the center for almost 6 hours, a small burst of deep convection with cloud tops colder than -80 deg C has developed since 0000 UTC just south of and over the previously exposed low-level circulation center. This recent convective development is the reason for keeping Grace as a 35-kt tropical storm. This intensity is supported by a Dvorak current intensity estimate of T2.5/35 kt from TAFB and a couple of 32-kt ASCAT-B wind vectors. The initial motion estimate is 275/17 kt. There is essentially no change to the previous forecast reasonings over the past couple of days. Grace is expected to gradually weaken and become more vertically shallow, and be steered quickly westward by the moderate low-level easterly trade wind flow on the south side of a deep-layer ridge. The official track forecast is just an update and extension of the previous advisory track, and lies close to the dynamical model consensus, TVCA. With increasing southwesterly to westerly vertical wind shear and an abundance of dry mid-level air ahead of Grace, steady weakening is expected due to these hostile environmental conditions. The only saving grace is the cyclone's robust low-level circulation, which could force periodic bursts of deep convection for the next 24 hours or so, similar to the most recent convective development. However, by 36 hours and beyond, westerly shear in excess of 25 kt should cause the circulation to weaken significantly due to less frequent and shorter duration convective bursts. Degeneration into a remnant low is expected by 48 hours, followed by dissipation in 96 hours. However, dissipation could occur sooner, similar to the ECMWF model solution. The new NHC intensity forecast closely follows the IVCN consensus model. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 14.0N 39.2W 35 KT 40 MPH 12H 08/1200Z 14.1N 41.8W 35 KT 40 MPH 24H 09/0000Z 14.3N 45.1W 30 KT 35 MPH 36H 09/1200Z 14.7N 48.4W 30 KT 35 MPH 48H 10/0000Z 15.1N 51.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 11/0000Z 16.0N 58.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/0000Z...DISSIPATED $$ Forecaster Stewart

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Hurricane LINDA Forecast Discussion Number 8

2015-09-07 22:32:51| National Hurricane Center (East Pacific)

Issued at 300 PM MDT MON SEP 07 2015 000 WTPZ45 KNHC 072032 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152015 300 PM MDT MON SEP 07 2015 After strengthening at a rapid pace for the past day or so, it appears that Linda's intensity is leveling off. The cloud pattern has not changed much since the last advisory and consists of a well organized central dense overcast with very cold cloud tops. There remains no evidence of an eye in geostationary satellite pictures, although a ragged eye is apparent in microwave images. The latest Dvorak classifications from TAFB and SAB are both 5.0/90 kt, so the initial wind speed is nudged upward to that value. Linda could strengthen a little more through tonight while it remains over warm water and in a moist and relatively low shear environment. After that time, however, cooler water and a dry and stable air mass should promote steady weakening. The new NHC intensity forecast is largely an update of the previous one and is in fair agreement with the intensity model consensus. This forecast calls for Linda to degenerate into a remnant low in about 4 days when the cyclone is expected to be over sea surface temperatures of about 24 deg C. The hurricane is still moving northwestward but at a slightly slower forward speed than earlier, 320/10 kt. A continued northwestward motion at about the same forward speed is predicted for the next 24 to 36 hours while a mid-level high pressure system remains centered over northern Mexico and the southern United States. After that time, the storm is expected to decelerate, as the high shifts westward and weakens, and then turn gradually westward once it becomes a shallow system by the end of the forecast period. The NHC track forecast is adjusted to the right of the previous one, especially at days 3-5, to come into better agreement with the latest consensus aids. Although Linda is forecast to remain well offshore of the Baja California peninsula, large swells are expected to affect portions of the west coast of that peninsula during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 18.3N 112.7W 90 KT 105 MPH 12H 08/0600Z 19.6N 113.7W 95 KT 110 MPH 24H 08/1800Z 21.2N 114.8W 90 KT 105 MPH 36H 09/0600Z 22.7N 115.8W 80 KT 90 MPH 48H 09/1800Z 24.0N 116.7W 65 KT 75 MPH 72H 10/1800Z 25.8N 118.9W 45 KT 50 MPH 96H 11/1800Z 26.4N 120.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 12/1800Z 26.4N 122.9W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Storm GRACE Forecast Discussion Number 9

2015-09-07 16:36:20| National Hurricane Center (Atlantic)

Issued at 1100 AM AST MON SEP 07 2015 000 WTNT42 KNHC 071436 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 1100 AM AST MON SEP 07 2015 Grace's cloud pattern has deteriorated somewhat this morning, with the deep convection becoming fragmented and banding features less evident than they were yesterday. The initial intensity is adjusted downward to 40 kt in agreement with data from a recent ASCAT overpass, and in line with the latest subjective Dvorak estimates from SAB and TAFB. An upper-level trough to the northwest of the tropical cyclone is producing some west-southwesterly vertical shear on Grace. The SHIPS model indicates that the shear will increase over the next several days, which should inhibit strengthening. The official intensity forecast calls for little change in strength during the next couple of days followed by gradual weakening. Grace is expected to degenerate into a remnant low by the end of the forecast period. This is similar to the intensity model consensus, IVCN, but given the current state of the system, Grace could weaken faster than indicated here. The storm is moving a little more quickly toward the west this morning, and the motion estimate is 275/15 kt. For the next several days, Grace will continue to be steered by the low- to mid-level flow to the south of the subtropical ridge. The GFS and ECMWF global models show a rather brisk westward motion, perhaps partially because the system opens up into a wave in the model predictions. The official forecast is a bit faster than the previous one and close to the latest model consensus. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 13.7N 35.9W 40 KT 45 MPH 12H 08/0000Z 13.9N 38.1W 40 KT 45 MPH 24H 08/1200Z 14.1N 41.5W 40 KT 45 MPH 36H 09/0000Z 14.5N 45.0W 40 KT 45 MPH 48H 09/1200Z 14.9N 48.1W 40 KT 45 MPH 72H 10/1200Z 15.5N 54.5W 35 KT 40 MPH 96H 11/1200Z 16.3N 61.0W 30 KT 35 MPH 120H 12/1200Z 17.0N 66.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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