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Hurricane LINDA Forecast Discussion Number 7

2015-09-07 16:33:14| National Hurricane Center (East Pacific)

Issued at 900 AM MDT MON SEP 07 2015 000 WTPZ45 KNHC 071433 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152015 900 AM MDT MON SEP 07 2015 Linda continues to gain strength. The cloud pattern consists of a well organized central dense overcast with very cold cloud tops and curved bands spiraling around it. There is no eye feature evident in satellite images, but a recent SSMIS microwave pass did indicate that an eye was present. A blend of the latest Dvorak T-numbers from TAFB/SAB and ADT values from UW-CIMSS support raising the initial intensity to 85 kt, making Linda a category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale. The rate of intensification of Linda has been an impressive 45 kt over the past 24 hours. The hurricane remains in a moist and relatively low wind shear environment and over 28-29 deg C waters. These favorable conditions should allow Linda to strengthen some more today, and it could reach major hurricane status by tonight. After that time, the waters begin to cool beneath the storm and environmental relative humidity values decrease. These more stable conditions should induce a weakening trend, and the cyclone is expected to become a remnant low in 4-5 days when it moves over sea surface temperatures of around 24 deg C. The NHC intensity forecast is slightly above the guidance in the short term, but falls in line with the intensity model consensus thereafter. Linda has been on a steady northwestward track at about 12 kt for the past 12-24 hours, steered by a mid-level high centered over northern Mexico and the southern United States. This motion is expected to continue for about another day as the steering pattern is maintained. 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 model guidance is in good agreement on this scenario, and only small changes were made to the previous track forecast. 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 07/1500Z 17.6N 112.2W 85 KT 100 MPH 12H 08/0000Z 19.2N 113.4W 100 KT 115 MPH 24H 08/1200Z 20.8N 114.7W 95 KT 110 MPH 36H 09/0000Z 22.2N 115.7W 85 KT 100 MPH 48H 09/1200Z 23.6N 116.6W 70 KT 80 MPH 72H 10/1200Z 25.7N 118.5W 50 KT 60 MPH 96H 11/1200Z 26.3N 120.7W 30 KT 35 MPH 120H 12/1200Z 26.1N 122.6W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Hurricane LINDA Forecast Discussion Number 6

2015-09-07 10:53:48| National Hurricane Center (East Pacific)

Issued at 300 AM MDT MON SEP 07 2015 000 WTPZ45 KNHC 070853 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152015 300 AM MDT MON SEP 07 2015 Linda has continued to rapidly strengthen overnight. An 0631 UTC GMI microwave overpass shows that a well-defined eye has developed within the very symmetric central dense overcast (CDO) feature that is seen in conventional satellite imagery. The eye has not yet become evident in the infrared satellite data. The initial wind speed has been increased to 75 kt, which is in agreement with the latest TAFB Dvorak classification and ADT intensity estimates from UW/CIMSS. Linda is likely to continue to rapidly strengthen today. The hurricane will be traversing very warm water and remain in a moist, low shear environment. The NHC intensity forecast now brings Linda to major hurricane strength in 24 hours, which is slightly above the intensity guidance. After that time, decreasing SSTs and less favorable thermodynamic factors are expected to cause weakening. A faster rate of decay is likely after 48 hours when Linda moves over SSTs below 26C and into a much more stable environment. The latter portion of the intensity forecast is essentially an update of the previous advisory and is close to the SHIPS model. The initial motion estimate is 315/12. The hurricane is forecast to move northwestward during the next 2 to 3 days around the western portion of a mid-level ridge that is centered over northern Mexico. After that time, a weaker Linda should turn west-northwestward, and then westward in the low to mid-level flow on the southern side of a low-level ridge. The track guidance is in good agreement on this scenario. The guidance has shifted a bit to the north at 72 hours and beyond, and the NHC forecast has been adjusted accordingly. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 16.7N 111.4W 75 KT 85 MPH 12H 07/1800Z 18.2N 112.6W 90 KT 105 MPH 24H 08/0600Z 20.0N 114.0W 100 KT 115 MPH 36H 08/1800Z 21.5N 115.1W 95 KT 110 MPH 48H 09/0600Z 22.8N 116.1W 80 KT 90 MPH 72H 10/0600Z 25.2N 118.0W 60 KT 70 MPH 96H 11/0600Z 26.0N 120.0W 35 KT 40 MPH 120H 12/0600Z 26.0N 122.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm GRACE Forecast Discussion Number 8

2015-09-07 10:38:48| National Hurricane Center (Atlantic)

Issued at 500 AM AST MON SEP 07 2015 000 WTNT42 KNHC 070838 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 500 AM AST MON SEP 07 2015 Deep convection has redeveloped near the center of Grace overnight, and an earlier SSMI microwave overpass showed that the convection was organized in a couple of bands around the center. There are indications in geostationary satellite imagery that the shear is beginning to increase as the cirrus outflow has become restricted over the western portion of the system. The initial wind speed remains 45 kt, which is in agreement with subjective Dvorak satellite intensity estimates from TAFB and SAB. Little change in strength is expected today. Environmental conditions are forecast to become less favorable by tonight as westerly vertical wind shear increases and dry mid-level air over the tropical Atlantic impinges on the circulation. The shear is forecast to increase to 20-30 kt by late Tuesday, and weakening is expected to begin by that time. The NHC intensity forecast is close to the LGEM model and the intensity consensus. Given the strong southwesterly upper-level winds expected near the eastern Caribbean late in the period, it is quite possible that Grace will degenerate to a tropical wave before it reaches the Lesser Antilles. Grace continues to move westward or 275/14 kt. The tropical cyclone is forecast to move generally westward to the south of a large mid- to upper-level ridge over the central Atlantic. The model guidance is in good agreement on this scenario and the NHC forecast is once again essentially an update of the previous NHC advisory. The new track forecast is close to the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 13.5N 33.9W 45 KT 50 MPH 12H 07/1800Z 13.7N 36.1W 45 KT 50 MPH 24H 08/0600Z 13.9N 39.1W 45 KT 50 MPH 36H 08/1800Z 14.2N 42.2W 45 KT 50 MPH 48H 09/0600Z 14.7N 45.4W 40 KT 45 MPH 72H 10/0600Z 15.5N 51.6W 35 KT 40 MPH 96H 11/0600Z 16.2N 57.2W 35 KT 40 MPH 120H 12/0600Z 16.8N 62.5W 30 KT 35 MPH $$ Forecaster Brown

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Hurricane LINDA Forecast Discussion Number 5

2015-09-07 04:53:46| National Hurricane Center (East Pacific)

Issued at 900 PM MDT SUN SEP 06 2015 000 WTPZ45 KNHC 070253 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152015 900 PM MDT SUN SEP 06 2015 Linda has been rapidly intensifying. Within the cyclone's sprawling circulation, a relatively small central dense overcast (CDO) has formed during the last 6 to 12 hours over the estimated low-level center. The deep convection within this feature has expanded in coverage, the associated cloud tops have cooled considerably, and its shape has become increasingly more symmetric. A 0110 UTC Windsat pass confirmed the rapid increase of inner-core structural organization, with a closed low-level ring of convection evident. A TAFB satellite classification of a T4.0/65 kt and the latest UW-CIMSS ADT value of 4.2/70 kt are used to raise the initial intensity to 65 kt. The current rapid intensification is likely to continue for another 24 hours or so, since Linda will be moving over anomalously warm waters of 28 to 29.5 deg C and embedded in a very moist environment. The only negative factor could be some northeasterly shear as indicated in SHIPS model output. However, this shear has not prevented Linda from strengthening much faster than the climatological rate of one T-number per day thus far. A more poleward and faster track forecast (described below) should bring Linda over cooler waters sooner, and increasingly unfavorable thermodynamic factors should cause rapid weakening to begin in 2 to 3 days. Remnant low status is shown at day 5, but it would not be surprising if it occurred earlier. The new intensity forecast is higher than the previous one and shows a peak intensity in 24 hours. Overall, it is just above the strongest guidance, the SHIPS and FSU Superensemble output, in the short term and near the multi-model consensus after that. Linda has been moving more poleward and faster, and the initial motion estimate is 320/12. Water vapor and upper-air analyses show a large mid-level anticyclone near the Texas-Mexico border, with a weakness in the ridge between 120-130W. Global models show Linda moving northwestward to north-northwestward toward the break in this ridge within a deep-layer southeasterly flow during the next couple of days. As the ridge weakens and shifts westward over northern Mexico in 2 to 3 days, Linda should continue northwestward but decelerate. The rapid weakening forecast to begin around that time should make Linda a progressively shallower cyclone, and its track is forecast to bend west-northwestward and westward by days 4 and 5 as it will then be under the influence of the low-level subtropical ridge. The new track forecast is shifted to the right and faster than the previous one through 72 hours, and is close to the multi-model consensus. By day 5, the track is slower and a bit to the left of the old forecast. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 16.1N 110.4W 65 KT 75 MPH 12H 07/1200Z 17.3N 111.6W 80 KT 90 MPH 24H 08/0000Z 19.2N 113.2W 95 KT 110 MPH 36H 08/1200Z 20.9N 114.7W 90 KT 105 MPH 48H 09/0000Z 22.1N 115.6W 80 KT 90 MPH 72H 10/0000Z 24.2N 117.6W 60 KT 70 MPH 96H 11/0000Z 25.0N 119.4W 35 KT 40 MPH 120H 12/0000Z 25.2N 122.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Tropical Storm GRACE Forecast Discussion Number 7

2015-09-07 04:50:45| National Hurricane Center (Atlantic)

Issued at 1100 PM AST SUN SEP 06 2015 000 WTNT42 KNHC 070250 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 1100 PM AST SUN SEP 06 2015 A partial ASCAT-B overpass at 2346 UTC, along with several passive microwave passes, indicates that Grace has a well-developed, compact low-level circulation that extends upward into the mid-levels of the cyclone. However, both conventional and microwave imagery also indicate that the inner-core convection has been significantly disrupted by the entrainment of dry mid-level air into the western and southern quadrants of the circulation, and has penetrated into the cyclone's center. The initial intensity of 45 kt, which could be generous, is based on Dvorak current intensity estimates of T3.0/45 kt from both TAFB and SAB, which is supported by a 40-kt ASCAT-B wind vector. Grace's motion continues to be 280/13 kt. The small tropical cyclone is expected to move a little north of due west throughout the forecast period due to moderate low- to mid-level easterly flow on the south side of a large subtropical ridge located to the north of Grace. The NHC model guidance is tightly packed around the previous advisory track, so the new forecast is just an update and extension of the previous advisory, and lies close to the consensus model, TVCN. Grace's fairly robust circulation should be able to mix out any dry air intrusions for the next 24 hours or so while the vertical wind shear remains low and, therefore, a return of inner-core deep convection is expected later tonight. Shortly after that time, however, the vertical shear is forecast by both the GFS and ECMWF models to increase to 25-30 kt from a westerly direction and for the mid-level humidity to decrease to near 40 percent, a combination that will halt any intensification and induce a steady weakening trend despite warm SSTs of near 28 deg C beneath the cyclone. The official intensity forecast is a little below the previous advisory forecast, and is similar to the intensity consensus model, IVCN. It is worth noting that the GFS and ECMWF models show significant weakening of the cyclone in 4 to 5 days, with possible dissipation occurring by 120 h. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 13.3N 32.5W 45 KT 50 MPH 12H 07/1200Z 13.5N 34.7W 45 KT 50 MPH 24H 08/0000Z 13.8N 37.7W 50 KT 60 MPH 36H 08/1200Z 14.0N 40.7W 45 KT 50 MPH 48H 09/0000Z 14.5N 44.0W 40 KT 45 MPH 72H 10/0000Z 15.3N 50.3W 40 KT 45 MPH 96H 11/0000Z 16.1N 56.5W 35 KT 40 MPH 120H 12/0000Z 17.2N 62.0W 30 KT 35 MPH $$ Forecaster Stewart

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